Kerry will press the case for punitive action against Syria after what the United States says was a chemical weapons attack by the regime of President Bashar al-Assad near Damascus, despite a lingering deep split among global powers.

On Friday, US President Barack Obama and Russian leader Vladimir Putin

failed to resolve their differences at the summit in Saint Petersburg as half of the G20 called for a "strong" response to last month's alleged chemical attack.

Kerry is to hold talks with the European Union's 28 foreign ministers in

Lithuania, which currently holds the EU's rotating chair, with the bloc itself sharply split.

Only France has said it is ready to take part in military action, while

Britain -- whose parliament voted against any involvement -- and Denmark have expressed support.

France was one of four European nations -- with Britain, Italy and Spain --that signed a statement Friday at the G20 meeting calling for a "strong international response" to the chemical attack widely attributed to the Assad regime.

The statement, signed by 11 of the G20 nations -- but not by Germany --

said the response would "send a clear message that this kind of atrocity can never be repeated".

It did not specify military action and European diplomats said the language remained unclear.

Obama said Friday in Saint Petersburg that the world could not "stand idly by" but Putin warned that it would be "outside the law" to attack without the UN's blessing.

Putin also said Russia would "help Syria" if the US were to strike,

pointing to existing military, economic and humanitarian cooperation.

Washington has prepared the ground for possible strikes, evacuating

non-essential embassy staff from Beirut and urging Americans to avoid all travel to Lebanon and southern Turkey.

As well as the stubborn international differences, the US administration

still has to win backing from Congress for any action against Syria.

Congress reconvenes on Monday and Obama addresses the nation on Tuesday.

But he acknowledged that convincing Congress to back military action against the Syrian regime would be a "heavy lift". "I understand the scepticism," the US president said.

The world is still waiting for a much-anticipated report by United Nations inspectors on the deadly August 21 attacks that left hundreds dead.

At the Russian summit, French President Francois Hollande vowed to wait for the UN report before joining any military action, a decision welcomed by Germany.

German Foreign Minister Guido Westerwelle urged the UN to publish its

report "as quickly as possible" to help Europe's divided leaders determine a response.

Sweden's Foreign Minister Carl Bildt told reporters it was essential to

wait for the UN report as "it will be the best picture we can get from any source".

"The Indians, the Brazilians, the Chinese and others don't really think

that information from US intelligence is enough, and that's the world we live in," he said.

Russia and China -- both veto-wielding permanent members of the UN Security Council -- have on three occasions voted down resolutions that would have put pressure on Assad. On Friday the Russian foreign ministry warned the United States against targeting Syria's chemical arsenal in any attacks.

Later Saturday, Kerry is due fly to Paris for talks with French officials. He will also meet Arab League leaders to update them on Syria and on progress in the Israeli-Palestinian peace process.

Pope Francis has appealed for a peaceful solution to the crisis, calling on the world to unite on Saturday in a day of fasting and prayer for Syria. He will lead the way with a five-hour vigil in St Peter's Square.