William Hague says the UK and US remain "closely aligned" on Syria, after talks with his US counterpart John Kerry.
The UK foreign secretary said the two were working together to save lives and revive peace talks as well as press for a strong response to the Assad government's use of chemical weapons.
Mr Kerry said the risks of doing nothing were greater than acting.
The two countries remained "true friends" despite the UK ruling out any military involvement, he insisted.
Their meeting in London comes as the US tries to gather support for military strikes.
UK Prime Minister David Cameron has said that Parliament's vote last month means the UK will not join the US in any military action in response to Syria's suspected use of chemical weapons.
After talks with the US Secretary of State in London, Mr Hague said the UK's position was clear but stressed that the government remained "highly active" on the diplomatic and humanitarian front and supportive of Washington's position.
He said 11 countries had signed a declaration following last week's G20 summit condemning the use of chemical weapons and calling for a robust response and urged other nations to follow suit to help increase pressure on the Syrian authorities.
Mr Kerry said the two countries' "special relationship" would not be affected by the UK's decision to reject military involvement, saying the bonds between the countries were "bigger than one vote or one moment in history".
Quoting the late Baroness Thatcher, he said the US and UK were "real, true friends" and the transatlantic relationship was "as relevant today as it has been in the past".
He dismissed suggestions that US President Obama had been forced to consult Congress after the UK Parliament rejected the case for a military response, suggesting he was intending to do this all the time and there was "no misinterpretation" of the British vote.
He also said he understood why the legacy of Iraq made many MPs nervous about getting involved in another conflict, saying he would have been "highly sympathetic" to that view if he had not seen the "compelling evidence" of the Assad government's guilt.
It "defied logic and common sense" to argue the opposition was responsible - as the Syrian authorities have claimed - and he defended the "limited" action the US was contemplating as being very different from the full-scale invasion of Iraq in 2003.
"We are not talking about war. We are not going to war. We will not have people at risk in that way."
Asked what would stop the US from acting, he said the Assad government would have to provide full international access to its stockpile of chemical weapons - a move he believed was highly unlikely.
The US secretary of state has warned that if there was no armed intervention Syria would use its chemical weapons again. But he also said the civil war in Syria could only be resolved by a political process.
The US accuses President Bashar al-Assad's forces of killing 1,429 people in a sarin gas attack in Damascus on 21 August. Mr Assad's government blames the attack on rebels fighting to overthrow him in the country's two-and-a-half-year civil war.
BBC diplomatic correspondent James Robbins said pictures of Mr Hague shoulder to shoulder with Mr Kerry could prove awkward for the Obama administration as it was a "vivid reminder" that a key ally had not been able to persuade its MPs of the need for action.
He said the talks may focus on ways to boost elements of the Syrian Opposition seen as moderates, he added.
Meanwhile, Mr Assad has reportedly again denied any link to the attack.
In an interview with the US broadcaster PBS, to be broadcast on Monday, he also reportedly "suggested that there would be, among people that are aligned with him, some kind of retaliation if a strike was made", PBS said.
France supports military intervention but it wants to wait for a report by UN weapons experts before taking action.
In a statement to MPs on last week's G20 summit in St Petersburg, David Cameron said he hoped the report would be delivered soon.
But he said the international community should not "over-estimate" its influence since the experts were not allowed to apportion blame and it was "already clear a war crime had taken place".
He said the UK would continue to try and "shape" the diplomatic and humanitarian response to the crisis while also providing technical and political support to moderate opposition groups.
Referring to the row during the G20 about reported comments by a senior Russian official about Britain's status, Labour leader Ed Miliband said he agreed with the PM that Britain was a "small island but a great nation" but added "it is a shame about the government".
Mr Cameron, he added, had failed to win support in the UK for arming Syrian rebels and for a "rush to war" but that Parliament and the public would support a concentrated diplomatic and humanitarian effort to reduce suffering in Syria.