DAMASCUS, Syria » Evidence of alleged chemical weapons use by the Syrian regime presented to Moscow by the U.S. and its allies is "absolutely unconvincing," Russia’s foreign minister said, as the Obama administration lobbied Congress to support a punitive military strike against Syria.

Foreign Minister Sergey Lavrov said "there was nothing specific there, no geographic coordinates, no names, no proof that the tests were carried out by the professionals." He did not describe the tests further.

President Barack Obama initially seemed poised to launch military action without asking Congress, but over the weekend changed his mind, a decision that delays any strike until after Congress returns from summer recess next week.

At issue in the escalating diplomatic confrontation between the U.S. and the regime of Syrian President Bashar Assad are alleged chemical weapons attacks on rebel-held areas in western and eastern suburbs of the Syrian capital of Damascus on Aug. 21.

The U.S. said it has proof that the Assad regime is behind attacks that Washington claims killed at least 1,429 people, including more than 400 children. Syrian officials have denied the allegations, blaming rebel fighters.

Lavrov brushed aside Western evidence of an alleged Syrian regime role. Russia, along with China and Iran, has staunchly backed Assad throughout the conflict.

"What our American, British and French partners showed us in the past and have showed just recently is absolutely unconvincing," Lavrov said at Russia’s top diplomatic school. "And when you ask for more detailed proof they say all of this is classified so we cannot show this to you."

On Sunday, U.S. Secretary of State John Kerry said the U.S. received new physical evidence in the form of blood and hair samples that show sarin gas was used in the Aug. 21 attack. It was not immediately clear whether that evidence had been shared with Russia.

U.N. chemical inspectors toured the stricken areas last week, collecting biological and soil samples, but it is not clear when the will present their findings.

Kerry said the case for an eventual military strike against Syria is getting stronger and that U.S. credibility is on the line.

However, the Obama administration so far failed to bring together a broad international coalition in support of military action, having so far only secured the support of France.

Britain’s parliament narrowly voted against British participation in a military strike last week, despite appeals by Prime Minister David Cameron, and the Arab League has stopped short of endorsing a Western strike against Syria.

In an emergency meeting on Sunday, the 22-state League called on the United Nations and the international community to take "deterrent" measures under international law to stop the Syrian regime’s crimes, but could not agree on whether to back U.S. military strikes.

Russia or China would likely veto any U.N. Security Council resolution sanctioning a Western strike against Syria.

China is "highly concerned" about possible unilateral military action against Syria and believes the international community must "avoid complicating the Syrian issue and dragging the Middle East down into further disaster," Foreign Ministry spokesman Hong Lei said today.

In Washington, the Obama administration was lobbying to secure domestic support.

Obama was to meet today with former political rival Sen. John McCain at the White House, hoping the foreign policy hawk will help sell the idea of U.S. military intervention.

On Capitol Hill, senior administration officials briefed lawmakers in private on Sunday to explain why the U.S. was compelled to act against Assad. Further meetings were planned from today to Wednesday.

The Syria conflict erupted in March 2011 as an uprising against Assad that quickly transformed into a civil war. More than 100,000 Syrians have been killed in the conflict.

In Damascus, the Syria representative of the U.N. refugee agency, Tarik Kurdi, said that five million Syrians have been displaced inside the country by the war.

In addition, nearly 2 million Syrians have fled to neighboring countries, according to previous U.N. figures, bringing the total number of uprooted Syrians to about 7 million, or nearly one-third the country’s estimated population of 23 million.

Kurdi said the need for aid is far greater than what the international community has provided so far.

"Whatever efforts we have exerted and whatever the U.N. has provided in humanitarian aid, it is only a drop in the sea of humanitarian needs in Syria," he told The Associated Press. The funding gap "is very, very wide," he added.

Vasilyeva reported from Moscow.