Media playback is unsupported on your device Media caption Michael Fallon: "We are briefing MPs on the very direct threat that Isil (IS) represents, not just in Iraq and Syria"

It is "morally indefensible" for Britain to rely on other countries to tackle the so-called Islamic State in Syria, Michael Fallon has said.

The defence secretary told BBC News he was appealing to MPs to reconsider the case for airstrikes.

It comes after a Russian passenger plane crashed in Egypt's Sinai desert last Saturday, which the UK government suspects was caused by a bomb.

In 2013, MPs rejected possible UK military action in Syria.

The vote two years ago was on potential airstrikes against the regime of President Bashar al-Assad, amid reports he had used chemical weapons, rather than militants from Islamic State (IS or ISIL).

The government is now making the case for Islamic State to be targeted, given its links to attacks on Western targets around the world, including the killing of 30 British holidaymakers in Tunisia in June.

The four-year civil war in Syria has ground to a stalemate, with President Bashar al-Assad's regime, so-called Islamic State, an array of Syrian rebels and Kurdish fighters all holding territory.

'Bite the bullet'

Mr Fallon told the newspaper that IS was a direct threat to the UK's national security and it was "very odd" that the UK was among a coalition of countries - including the US, France and Australia - fighting IS militants in Iraq but was not doing the same in Syria, where the group is based and co-ordinates its wider military operations from.

"That is morally indefensible that our streets should be protected by French, Australian and American aircraft, when we are not prepared to bite the bullet and get the Tornados dealing with these supply routes," he said.

Asked whether it would strengthen the case for British if IS was found to be responsible for bringing the Russian airliner down, he replied: "We don't know whether it was Isil. If it turns out to be Isil, of course."

Last year, Parliament approved UK airstrikes against IS targets in Iraq but ministers have said they will only seek MPs' approval to extend the action to Syria if there is a political "consensus" behind the action.

For more than a year, the US and coalition forces have been carrying out air strikes against IS, which controls a large part of northern Syria and parts of neighbouring Iraq.

'New Parliament'

And Russia began bombing rebels in Syria in September, with President Vladimir Putin saying the aim was to "stabilise the legitimate authority" of President Assad.

In a separate interview with the BBC, Mr Fallon dismissed recent media reports that a new vote on Syria has been dropped, saying it would be held when "we are pretty sure we can win".

Image copyright PA Image caption MPs have so far rejected the idea of the RAF bombing IS targets in Syria

"We've had 30 British holidaymakers slaughtered on a beach in Tunisia, and it's not right morally to rely on French or Australian or American aircraft to keep our streets safe," he told the BBC's defence correspondent Jonathan Beale.

"In the end, we have to be prepared to strike at ISIL headquarters, which is in Syria and not in Iraq... This is a new parliament, and we are continuing to work to build a consensus that would give us the authority to strikes at the heart of ISIL in north-east Syria."

'Clear rationale'

Downing Street said the prime minister's position had not changed.

"The prime minister has set out very clearly his view that there is a clear rationale for taking military action in Syria but equally, he has always made clear that to do that would require the consensus of the House," a spokesman said.

The Russian Metrojet Airbus A321 was flying from Sharm el-Sheikh to St Petersburg when it crashed, killing all 224 people on board, on Saturday.

UK investigators believe a bomb was put in the hold prior to take-off, the BBC has learned.

On Tuesday, the influential Foreign Affairs Committee - which has a Conservative majority - urged David Cameron not to press ahead with a vote on UK air strikes against Islamic State militants in Syria.

The committee of MPs said no vote should take place on Syria until the government presents a "coherent international strategy" to defeat IS and end the country's civil war.

The Labour leadership is currently opposed to extending air strikes, as are the SNP, while several Tory MPs harbour doubts about the move - making it unlikely that the government could win a vote.