VILNIUS, Lithuania  — Secretary of State John Kerry failed to sway his European counterparts on the urgency of a U.S.-led military strike to halt the use of chemical weapons in Syria’s 2 1/2-year civil war.

France, the principal U.S. ally in a possible assault, slowed its march to a confrontation by backing a European Union appeal to put off an armed response until the United Nations delivers a report on last month’s use of chemical agents in a massacre near Damascus.

“The EU underscores at the same time the need to move forward with addressing the Syrian crisis through the UN process,” the 28-nation bloc’s foreign-policy chief Catherine Ashton told reporters after EU foreign ministers met Kerry in Vilnius, Lithuania.

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U.S. setbacks in securing international backing for targeted strikes on Syria’s war-making capability were matched by President Barack Obama’s trouble at home in persuading Congress to authorize an American intervention.

Kerry thanked the EU for “a strong statement about the need for accountability,” then left Vilnius for Paris to meet French leaders tonight and Arab League foreign ministers tomorrow. Kerry then goes to London to consult British and Saudi officials, and to meet Palestinian Authority President Mahmoud Abbas.

Obama will make his case to voters on Sept. 10. In a preview of that speech, he said in his weekly radio address today that the failure to punish Syria’s chemical weapons use would embolden terrorists and rogue states and “pose a serious threat to our national security.”

A Group of 20 summit in Russia that ended yesterday exposed international divisions, with resistance led by Russian President Vladimir Putin, the prime ally of Syrian President Bashar al-Assad.

While Putin’s objections echoed Russia’s opposition to the U.S.-led Iraq invasion in 2003 and underlined current strains between Moscow and Washington, the European doubts about the case for war came from putative U.S. allies.

The buildup toward another intervention by Western powers in the Middle East has pushed oil prices to a two-year high. West Texas Intermediate crude rose 2 percent to $110.53 per barrel yesterday.

France and Britain have both produced intelligence dossiers backing U.S. assertions that Assad’s forces were probably behind a chemical attack near Damascus on Aug. 21 that killed more than 1,400 people.

France, which teamed with Germany and Russia to oppose the Iraq war, emerged as the principal European voice in favor of military intervention in Syria after U.K. Prime Minister David Cameron’s call for a British fighting role was repudiated by parliament in London.

The full EU allowed only that the intelligence “seems to indicate” that Assad’s regime was the culprit of what it called a “blatant violation of international law, a war crime and a crime against humanity,” according to Ashton. The EU urged waiting until UN laboratories establish the facts of the Aug. 21 massacre. A UN report is due later this month.

While the European officials didn’t ask Kerry to commit to a delay, Ashton said he will go back to Washington and “think about what we were saying.”

EU divisions pit France and Denmark, among the most vocal supporters of a military response, against Germany, a European diplomat present in the meetings told reporters. Some fear a strike could create a rally-around-Assad effect in Damascus, said the diplomat, who wasn’t authorized to speak publicly.

Europe’s misgivings centered on France, which completed a 24-hour policy reversal today. On arriving in Vilnius yesterday, Foreign Minister Laurent Fabius said he saw no point in waiting for the UN report because “everyone knows” that chemical weapons were used east of Damascus and that the UN won’t resolve the question of who used them.

After the G-20 summit in St. Petersburg, French President Francois Hollande contradicted his foreign minister, saying France too would wait to hear from the UN analysts.

The EU “hopes a preliminary report of this first investigation can be released as soon as possible and welcomes President Hollande’s statement to wait for this report before any further action,” Ashton said.

Hollande remained on board with a possible military strike, saying it would “accelerate a political solution” to a conflict that has left more than 100,000 dead. France would arm the rebels if Congress rejects a U.S. intervention, he said.

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