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.
Yesterday, US President Barack Obama and Russian leader Vladimir Putin failed to bridge their differences at the summit of top global powers in Saint Petersburg.
Just over half of the G20 states signed up to a statement calling for a "strong" response to last month's alleged chemical attack.
"The costs of inaction here are much greater than the costs of action," he wrote in yesterday's Huffington Post.
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 at the G20 meeting yesterday calling for a "strong international response" to the chemical attack, widely attributed to the Assad regime.
It did not specify military action and European diplomats said the language remained vague.
But while Obama said the world could not "stand idly by", Putin warned 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.
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.
Obama made several calls to Republican and Democratic lawmakers during his flight home from Russia, a senior administration official said, declining to elaborate.
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".
