David Cameron has signalled his support for Barack Obama over Syria after the US president said he would ask Congress to vote on military strike action.

In a tweet, the prime minister said: “I understand and support Barack Obama’s position on #Syria.”

Foreign Secretary William Hague called it a “fine speech” after President Obama outlined his position for action on the war-torn country.

A former Lib Dem leader said Parliament could “reconsider its position”.

It comes after British MPs defeated a government motion to take part in any military action in Syria on Thursday evening, effectively ruling out UK support in a US strike.

The US says the Syrian government carried out chemical weapons attacks on 21 August in which 1,429 people died.

Syrian President Bashar al-Assad – who denies any involvement, blaming opposition forces – has said his country will defend itself against any Western “aggression”.

‘Off agenda’

Speaking after the US president set out his position, former Liberal Democrat leader Lord Ashdown said: “This was a brave and principled act from a brave and principled president.”

He added: “It opens up all sorts of different new possibilities. One of which is the UK Parliament certainly could reconsider its position. It puts huge pressure on Mr Miliband.

“What now if having followed further discussions with [Russian President] Putin and Congress giving its view, what now will Mr Miliband say if there is a UN process?

“If Congress says yes, does Mr Miliband continue to say no?”

Mr Miliband has not commented on the president’s speech but the Labour leader has said that he does not believe that the House of Commons vote means that the UK could not make a difference to “innocent civilians” in Syria.

The BBC’s political correspondent Ross Hawkins said a Labour source told him that “this is a matter for President Obama”.

“We set out clear criteria for British military action. Going to Congress is a matter for President Obama.”

Asked whether the issue could return to the Commons, the source said: “That is not a matter for us. It is the PM who took it off the agenda.”

‘Closest ally’

Speaking outside the White House, President Obama said he was “confident” that the US government had made a case for military action without the need to wait for United Nations inspectors to compile their report.

He added he was comfortable going forward without the support of the UN Security Council “that, so far, has been completely paralysed and unwilling to hold [Syrian President] Assad accountable”.

“As a consequence, many people have advised against taking this decision to Congress and undoubtedly they were impacted by what we saw happen in the United Kingdom this week when the Parliament of our closest ally failed to pass a resolution with a similar goal, even as the prime minister supported taking action.

“Yet, while I believe I have the authority to carry out this action without specific congressional authorisation I know that the country will be stronger if we take this course and our actions will be even more effective.”

President Obama also appeared to signal the “special relationship” between the US and the UK was not beyond repair after MPs voted against military action on Thursday, referring to Britain as “our closest ally”.