By Luke Baker
ST. PETERSBURG, Russia (Reuters) - Europe's top officials stopped short on Thursday of endorsing a U.S.-led push for a military strike against Syria in response to last month's chemical weapons attack, and warned there could be no military solution to the 2-1/2-year-old conflict.
The position set out by European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso would appear to leave the European Union at slight odds with the United States, as President Barack Obama has said he is poised to take military action once he has approval from the U.S. Congress, where votes are expected next week.
Van Rompuy described the August 21 poison gas attack near Damascus, in which an estimated 1,400 people died, as "abhorrent" and a crime against humanity that could not be ignored. But ultimately diplomacy remained the best way to resolve a conflict which has killed 100,000 people, he said.
"There is no military solution to the Syrian conflict," Van Rompuy told reporters ahead of a summit of the Group of 20 countries in St Petersburg, where Syria is expected to dominate debate along with discussion on the global economy.
"While respecting the recent calls for action, we underscore at the same time the need to move forward with addressing the Syrian crisis through the U.N. process."
Van Rompuy did not explicitly oppose a military response, which France and Britain publicly support, and officials indicated that a final position was still evolving.
Obama has been keen to garner the broadest possible allied and international support for any military action.
European Union leaders in the G20 were expected to discuss the issue on the sidelines of the two-day summit, with officials saying Obama would try to convince the EU of the need for immediate action during the summit dinner on Thursday evening.
"The international community cannot remain idle," Van Rompuy said, a comment that appeared to leave the door open. "We have to show that such crimes are unacceptable and will not be tolerated, to show that there can be no impunity."
Van Rompuy's stance also hinted at differences within the EU. France, which with Britain is the most influential of the EU's 28 member states on foreign policy, has said it will support any military action taken by Washington.
British Prime Minister David Cameron was also keen to support military intervention, but he lost a parliamentary vote on the issue last week and Britain will not take part.
The position set out by Van Rompuy and Barroso effectively calls for the main effort of the international community to be to work through the United Nations in determining how to contain Syrian President Bashar al-Assad and his forces.
Putin, an ally of Assad who has condemned the U.S. rush to action, has goaded U.S. officials for the mistakes made in Iraq and Afghanistan. He has also accused NATO of exceeding the bounds of a 2011 U.N. mandate for intervention in Libya.
In an interview with the Associated Press ahead of the G20, Putin did not rule out military action against Syria if there was proof that Assad's forces carried out the chemical attack and such action was approved by the U.N. Security Council.
Van Rompuy said he had no reason to doubt the credibility of the evidence presented by the United States indicating Assad's forces released the chemical weapons. But he said it was essential to wait until U.N. experts had concluded an on-the-ground investigation into the attack with a report.
"I look forward to the information the U.N. secretary general will share with us on this matter later today," he said. "It is important that at least a preliminary report is released as early as possible."
EU foreign ministers meet in Vilnius on Friday and Saturday and will weigh the situation in Syria, among other issues. U.S. Secretary of State John Kerry will join them and is expected to push the case for military action.
While France has made clear its support for a U.S.-led response, and Denmark has given similar indications, most other EU member states have either not spoken up or have privately expressed reservations about an armed retaliation.
Barroso said diplomacy, including renewed efforts towards a Syria peace conference in Geneva, was the only way ultimately to bring the conflict to an end.
(Editing by Mark Heinrich)