Image copyright AFP Image caption Islamic State - sometimes known as Isis or Isil - has made rapid gains in Syria and Iraq since June

Number 10 has insisted possible military action against Islamic State (IS) in Syria has not been ruled out.

Earlier Foreign Secretary Philip Hammond said MPs had voted last year against air strikes there and that decision would not be revisited.

Number 10 said he had been referring to strikes against the Syrian regime.

It comes after US President Obama pledged to "degrade" and "destroy" IS in Syria - including with a systematic campaign of air strikes.

Foreign Affairs Select Committee member John Baron called on the prime minister to clarify the British government's position on what was a matter of "seminal performance".

My instinct is the government will propose air strikes Richard Ottaway, Foreign Affairs Select Committee

The Tory MP said there appeared to be a "disparity between the foreign secretary and Number 10".

'Unity of approach'

The US has already launched more than 150 air strikes against IS, formerly known as ISIL, in Iraq and provided arms to Iraqi and Kurdish forces.

IS controls large parts of Syria and Iraq after a rapid military advance.

Its fighters have become notorious for their brutality, beheading enemy soldiers and Western journalists on video.

As part of the US strategy for tackling the jihadists, President Obama announced on Wednesday that 475 military personnel would be sent to Iraq in a non-combat role.

President Obama's anti-IS strategy

A systematic campaign of air strikes against IS targets "wherever they are", including in Syria

Increased support for allied ground forces fighting against IS - but not President Assad of Syria

More counter-terrorism efforts to cut off the group's funding and help stem the flow of fighters into the Middle East

Continuing humanitarian assistance to civilians affected by the IS advance

In Berlin earlier, Mr Hammond told reporters: "Let me be clear, Britain will not be taking part in any air strikes in Syria, I can be very clear about that.

"We've already had that discussion in our Parliament last year and we won't be revisiting that position."

Media playback is unsupported on your device Media caption Philip Hammond: "Britain will not be taking part in any air strikes in Syria"

But Downing Street later clarified that "the point he was making" was that MPs had already voted to oppose "air strikes against the [Syrian President Bashar al-]Assad regime".

"In terms of air power and the like, the prime minister has not ruled anything out," a Number 10 spokesman said.

"That is the position. No decisions have been taken in that regard."

Number 10 has welcomed President Obama's "tough, long-term, intelligent" strategy in tackling IS and has said the US and UK would continue their "unity of approach".

BBC deputy political editor James Landale said Mr Hammond had "got it wrong".

"The first rule of British diplomacy is don't disagree with the American president just after he's announced a new foreign policy," he said.

"That's what the foreign secretary found himself doing today. That's why he was over-ruled by the people who work in there."

'Gross violation'

In the UK, chairman of the Foreign Affairs Select Committee, Richard Ottaway, said he believed MPs would support the bombing of targets in Iraq.

"My instinct is the government will propose air strikes," the Conservative MP told BBC News.

"They will put it to Parliament and my instinct is that Parliament will approve it."

And on Syria he added: "If the argument's put that this is to eliminate the cancer of ISIL, I suspect Parliament will support strikes in Syria against ISIL."

On Wednesday Mr Hammond told MPs any attack on Syria would constitute a higher-risk strategy than taking action in Iraq, adding there was a "qualitative difference" between bombing the two countries.

"The legal, technical and military differences make the proposition of air strikes an order of magnitude more complicated in Syria," he said.

Meanwhile the Ministry of Defence said weapons and ammunition provided by the UK to Kurdish fighters in northern Iraq had arrived in Irbil.

The weaponry includes heavy machine guns and almost half a million rounds of ammunition.

"This will give the Kurdish Peshmerga additional firepower in order to help them defend the front line, protect civilians and push back ISIL advances," the MoD said in a statement.

"The UK will continue to look positively on any further direct requests for assistance to the Kurds."

Image copyright Reuters Image caption US Secretary of State John Kerry arrived in the Red Sea port of Jeddah on Thursday

US Secretary of State John Kerry is in Saudi Arabia as he seeks to build a regional coalition against IS.

A joint statement issued after talks in Jeddah declared a "shared commitment to stand united against the threat posed by all terrorism" including IS.

In addition to Saudi Arabia, Arab states taking part were Bahrain, Egypt, Iraq, Jordan, Kuwait, Lebanon, Oman, Qatar and the United Arab Emirates. Nato member Turkey was also represented, but did not sign the statement.

Russia, which has been an ally of President al-Assad, has warned that any US bombing of IS positions in the country would be "an act of aggression, a gross violation of international law".