Britain will consider military intervention in Syria's bloody civil war, with contingency plans being drawn up into President Bashar Assad's alleged use of chemical weapons.
Here is a Q&A examining the military options open to the UK, the US and the West in any attempts to bring an end to the conflict.
Could troops be used to create and guard 'safe zones'?
The creation of so-called "buffer" or "safe zones" would see some of Syria's borders with neighbouring countries used to create makeshift camps for refugees. However, such zones would require stringent efforts to defend the camps from air, missile and ground attacks. Some countries may be unwilling to see such a zone established on their border with Syria, through fear the violence will spread closer to their land. Some neighbours, such as Turkey, already feel as though the conflict is heavily involving their country.
Would a no-fly zone restrict air strikes?
The Assad regime has meted out violence both from ground level through tanks and shells, as well as air strikes. An allied forces-enforced no-fly zone has been suggested as a means of preventing the bombing of large swathes of civilian population, as well as aiming to reduce air strikes on rebel bases. Yet they could be difficult to enforce, and are deemed "insufficient" alone in restraining regime forces without targeting ground forces as well. Russia has already said any attempt to enforce a no-fly zone over Syria from Jordan would violate international law.
Should the military target Syria's weaponry?
Syria is thought to have some of the world's largest stocks of chemical weapons, including mustard gas and the nerve agent sarin, although the government in Damascus has refused to confirm it. The regime is believed to hold significant quantities of these in reserve, scattered at bases throughout the country - one of the few in the world not to have outlawed the use of chemical weapons. Targeting and either destroying or securing the stock would prevent it being used on civilians or by terrorists, though the fact that little is known about where it is stored would make finding it extremely difficult. The sheer number of military personnel required to complete the operation could also make it hard to carry out.
Would President Assad be targeted?
He was recently the subject of an assassination attempt, though the attack on his motorcade ended up injuring only Assad's bodyguards. Military experts reckon Western forces would be more likely to go for other regime targets so as not to influence the outcome of a civil war through taking out Assad.
What arms are available to the military?
Experts agree a "boots-on-the-ground" approach would be high-risk and largely unpalatable with the British public - with many still questioning Tony Blair's decision for British troops to join the US-led action in Iraq a decade ago. Instead Western forces including the Americans and French military could favour using cruise missiles, which are capable of delivering pinpoint strikes from 1,240 miles (2,000km). With submarines already positioned in the Mediterranean, it would be possible for Britain's military effort to be coordinated from the sea. Details of Britain's contingency plans remain secret, though the Ministry of Defence this afternoon said a planned Royal Air Force training mission involving the Typhoon fighter jets had been postponed. The jets were to have been deployed on the Mediterranean island of Cyprus.
What are the dangers?
Sending an influx of British, American or other Western troops to Syria - or indeed other parts of the Arab world - would undoubtedly attract enemy attacks, including raising the prospect of suicide bombings. It is more likely that air launch missiles would be deployed in order to reduce the risk of military casualties.
What stumbling blocks could hinder international involvement?
Efforts to achieve United Nations backing for any British military action against Assad would be hampered by the opposition of Russia, which could veto any resolution against its ally. The split over the use of chemical weaponry, and whether Assad has been responsible, is characterised by the fact David Cameron and his Russian counterpart Vladimir Putin continue to clash over evidence of such an attack. Assad denies using the weapons and Moscow - a key regime ally which supplies arms to Syria - has backed claims that video footage of victims could be opposition propaganda. Going to war without a UN mandate has already concerned Barack Obama.
What hopes are there of military action being successful?
Some Western analysts say any action against Syria would be "symbolic and punitive". But any operation in the heartlands of Syrian conflict would be fraught with difficulty - the UN having confirmed that chemical weapons experts, who were trying to investigate a deadly attack blamed by Western nations on Assad's regime, have been "deliberately shot at multiple times" in Damascus. Shocking images beamed around the globe in recent days have shown, in graphic detail, the cost that a chemical attack has on the human body.