DAMASCUS—Arab leaders said Tuesday that Syria had used chemical weapons against its population, while Western governments discussed military responses to the attacks, bolstering the case for U.S. military strikes against the regime of Syrian President Bashar al-Assad.

The Arab League demanded an international response to what it called the “heinous crime” of last week’s alleged chemical attack near Damascus that activists and rebels said left more than 1,000 Syrians dead. But the U.S.’s major Arab allies have stopped short of offering public support for a strike without international backing, reflecting broad unease in the region about another Western military intervention.

This suggests the U.S. would face no opposition from regional allies if things go smoothly, and leaves Arab governments with political cover if things go badly.

“Don’t expect a big cheer from us,” said Abdulkhaleq Abdullah, a political-science professor in Dubai, of the likely response from the region. “If the results are fine, and the damage is very limited, I think that is gonna be a good sign. Maybe, ‘Wow, give America a D.’ ”

The U.S. is examining ways to attack Syria without the approval of the United Nations, where Russia would likely veto any military action, U.S. and European officials have said. The Obama administration has recently stepped up contacts with North Atlantic Treaty Organization and Arab League allies about supporting a military operation against Damascus. On Tuesday, U.S. Defense Secretary Chuck Hagel spoke with his opposites in France and the U.K., according to defense officials.

The U.S. Defense Department has presented military options to PresidentBarack Obama, Mr. Hagel said, without outlining them. Defense officials have said the U.S. is considering cruise-missile strikes from navy ships in the Mediterranean.

“We are ready to go,” Mr. Hagel said.

Arab League delegates on Tuesday urged the U.N. Security Council, rather than the West, to take “deterrent” action against Syria to prevent a repeat of alleged chemical attacks on Aug. 21 in the suburbs of Damascus.

Even Saudi Arabia and other countries that have helped arm, train and fund rebels fighting Mr. Assad have declined to offer public endorsement for any Western-led attack.

While senior Saudi officials have been urging the U.S. and others behind the scenes to support tougher action in Syria, according to officials, Arab leaders for more than a year have publicly maintained that any international military action there should be sanctioned by the Security Council.

A harder line emerged from some Western capitals.

France’s President François Hollande vowed Tuesday to “punish” the Assad regime. “This mass chemical massacre cannot go unanswered,” he said.

Addressing ambassadors at the Élysée Palace, Mr. Hollande pressed his case for the West to respond to the attack with “necessary force” targeting the Assad regime. He hinted that France was open to supporting a military strike without a Security Council resolution—a step that French officials had previously said would be essential. “International law must evolve with its times. It can’t be a pretext for allowing massacres to be perpetrated,” Mr. Hollande said.

The U.K. military is drawing up plans for a possible response to the alleged attack, the government said Tuesday.

But Prime Minister David Cameron said any British action in Syria would have to be legal, proportionate and specifically about deterring future global chemical-weapons use.

“This is not about getting involved in a Middle Eastern war or changing our stance in Syria or going further into that conflict,” he said in a recorded interview with BBC television. “It is about chemical weapons. Their use is wrong and the world shouldn’t stand idly by.”

On Tuesday, Vice President Joe Biden said there was no question that the Assad regime was behind the attack.

“There is no doubt that an essential international norm has been violated,” Mr. Biden said at the American Legion’s annual convention in Houston. “No one doubts that innocent men, women and children have been the victims of chemical-weapons attacks in Syria. And there is no doubt who is responsible for this heinous use of chemical weapons in Syria: the Syrian regime.”

U.S. officials have said they expect to release evidence in coming days that Syria’s regime was behind the attacks.

Syria “utterly and completely” rejects the allegations that it used chemical weapons, Syrian Foreign Minister Walid al-Moallem said on Tuesday. He added that Syria would defend itself by means available. “We will surprise others” planning to attack Damascus, he said.

“We are hearing the drums of war,” Mr. Moallem added. “They want to attack Syria. I believe to use chemical weapons as a pretext is trite and inaccurate.”

Syria’s foreign minister condemned the U.S. for flouting international law and ignoring a continuing U.N. investigation into the incident, which has yet to determine whether chemical weapons were used.

In Cairo, Egypt Foreign Minister Nabil Fahmy appeared to side against intervention, saying on Tuesday, “The solution for Syria must be diplomatic, not militaristic.”

Turkey, in a newspaper interview by Foreign Minister Ahmet Davutoglu published Monday, became the first major Muslim Middle East ally of the U.S. to announce it would join an international military coalition against Syria, even without advance U.N. approval.

The weakest Arab states, Lebanon and Jordan, particularly fear possible retaliation and a further deluge of Syrian refugees in the event of a Syria strike.

A meeting of U.S., Saudi, and other Western and regional top military officials in the Jordanian capital on Sunday and Monday was devoted mainly to reassuring Jordan of protection in the event of any disruption following a strike on Syria, as well as to try to plot responses to any further alleged use of chemical weapons by Syria, according to officials in Jordan and in the Gulf familiar with the proceedings.

In Jordan, where a U.S.- and Saudi-backed effort is helping train Syrian rebels, Jordanian King Abdullah publicly called for peaceful settlement. Jordan already has taken in hundreds of thousands of refugees from Syria. Its fear is being “dragged into retaliation and war,” a senior Jordanian official said.

Saudi Arabia—for more than a year the strongest advocate of international action on Syria—has limited its public response to last week’s alleged chemical attack to statements by Foreign Minister Saud al-Faisal calling for unspecified, decisive action under the U.N.

A Saudi cabinet statement repeated that position Monday night, after the U.S. made clear it was considering a military strike on Syria.

“Not yet,” a Saudi government spokesman said, when asked if the government had said if it would support a military strike on Syria.

In principle, and in private, Saudi Arabia probably “would support any act to stop that war, or stop the use of gas,” said Anwar Eshki, a former adviser to Saudi Arabia’s council of ministers, or cabinet, and the head of a Saudi-based strategic research center. Mr. Eshki was referring to the use of poison gas.

A U.N. team is currently in Damascus investigating the suspected chemical-weapons attacks that hit several towns on the capital’s outskirts last week, whose victims included children and women, according to witnesses. On Monday, the U.N. was granted access to one of those sites, Mouadhamiya, to conduct interviews with survivors and take soil samples, although their convoy was fired on by unknown snipers earlier that day.

A second trip planned by the U.N. team was canceled Tuesday after a disagreement by rebels over how to provide security to the international inspectors, the foreign minister said. The U.N. said that its team decided to postpone its visit by one day “in order to improve preparedness and safety for the team,” but didn’t speak to Mr. Moallem’s claims.

Access to the areas has been complicated by a Syria military operation—code-named Operation City Shield—that kicked off just hours after the first reports that toxic gas was killing residents.

For months, Syrian forces have successfully fought to regain control over the suburban regions surrounding the capital Damascus. The Eastern Ghouta region where the suspected chemical attack occurred is the last remaining area not under partial or total regime control.

Mr. Moallem, the foreign minister, said that the government launched a “pre-emptive strike” before rebels made claims about chemical weapons use last week. He said that the government had intelligence showing that rebel fighters trained outside Syria were amassing in that district “to raid Damascus.” The military’s assault was before Aug. 21, when the chemical attacks were alleged to have occured, but he declined to specify when.

Security officials previously said the strike was in the first hours of Aug. 21 and that rebels had been planning a massive attack on Damascus from four different fronts.

Mr. Moallem said the current government operation in Damascus would continue and would not be affected by plans by the U.S. and its allies to attack the regime.

“The military effort won’t stop, they are dreaming if they want to limit the victories of the armed forces,” said Mr. Moallem.