Syrian President Bashar al-Assad REUTERS/Benoit Tessier Sweden and Poland warned against knee-jerk reactions to the crisis in Syria on Saturday, saying that any international effort to solve it will require a commitment "for decades to come".

Speaking at a regional NATO conference in the Latvian capital, Riga, Swedish Foreign Minister Carl Bildt said the West was being short-sighted regarding the instability sweeping the Middle East.

"Let's be realistic. We have an escalating civil war in the entire Levant...the only thing I can say that would have a reasonable chance of success would be to go in with armies and stay there for 30 years and try to do some real nation building. Appetite for that? Non existent," Bildt said.

"It is an immensely complex problem. There is not a simple solution. We will have, on the European side, to stay engaged with this part of the world for decades to come in every single respect," Bildt added.

Polish Foreign Minister Radoslaw Sikorski pointed to previous Western interventions in Libya and Iraq as a reason for caution.

"Do you really want us to do another Iraq? Was that really such a good idea? Was it worth the [spoils of war] and the blood that was expended there?" Sikorski asked an audience consisting chiefly of foreign policy experts, urging them to "think about the consequences before we plunge in".

Sikorski said US President Barack Obama had "done the right thing" in referring the matter of military action against the Assad regime to Congress, but had strong words for the United Nations Security Council, accusing it of failing its obligation to act as "the voice of all humanity".

"The Security Council is simply not doing what it is supposed to be doing, which is not to be a place where selfish nations look after their interests... I can't think of a better case where the voice of humanity should be heard other than to protest against the use of these (chemical) weapons," Sikorski said.

China and Syrian ally Russia have repeatedly used their veto power on the UN Security Council to block both military action and international criminal proceedings against Syrian President Bashar al-Assad.

European Union nations Saturday called for a "strong" response in the Syria crisis but stopped short of endorsing possible military action by the United States over the alleged use of chemical weapons by Damascus.

The EU also urged the Security Council "to fulfil its responsibilities", a reference to Russia and China's refusal to sanction Assad.

A staunch US ally in both the Afghanistan and Iraq wars, Poland has ruled out taking part in any military intervention in Syria.

Sweden has said it would only support military action if it were backed by a UN mandate.

US Secretary of State John Kerry on Saturday made clear that Washington had not decided to postpone a decision on military action until the release of the UN report on who was behind the deadly August chemical weapons attack on a Damascus suburb.