The International Committee of the Red Cross says the conflict in Syria should be treated as a full-blown civil war.

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The humanitarian organisation's spokesman Hicham Hassan said: "We are now talking about a non-international armed conflict in the country. Hostilities have spread to other areas of the country.

"International humanitarian law applies to all areas where hostilities are taking place."

The ICRC had restricted its assessment of the scope of the conflict to the hotspots of Idlib, Homs and Hama, but the organisation is now acknowledging that the violence is more widespread.

The Geneva-based group's assessment may also have far-reaching legal implications.

As a "non-international armed conflict", the fighting in Syria comes under Common Article 3 of the Geneva Conventions, with both sides obliged to respect the "rules of war".

Torture, the mistreatment of civilians and the denial of medical treatment to the wounded are all outlawed under the conventions, and prosecutions for war crimes are more likely if a conflict is considered a civil war.

A Foreign Office spokesman told Channel 4 News: "This will have serious legal and policy ramifications". But he added: "We don't need a label to know how dire the situation in Syria is."

The news comes as UN observers continue to investigate claims that more than 200 people were massacred by Syrian government forces in the village of Tremseh on Thursday.

The team found blood, burned homes and signs of artillery fire but were unable to confirm the number of casualties.

The attack appeared to target the homes of opponents of the Assad regime and army defectors, a spokesman said yesterday.

Syria's Foreign Ministry later said 37 fighters and two civilians had been killed in clashes in Tremseh, far less than the death toll claimed by the opposition.

The ministry has rejected UN envoy Kofi Annan's claims that helicopters, tanks and artillery were used in the attack.

Sausan Ghosheh, a spokeswoman for the UN mission in Damascus, said on Sunday: "We can confirm that there was a military operation on July 12th, on Thursday. The attacks appeared targeted towards specific homes of activists as well as army defectors.

"Our UN team there observed homes which had pools of blood and blood splatters in some of the rooms as well as empty bullet cases. There was a wide range of weapons used including heavy weapons and artillery, mortar and small arms."

Russian President Vladimir Putin will meet Mr Annan in Moscow on Tuesday for talks on the conflict in Syria, a Kremlin statement said on Sunday.

The statement said: "During the course of the upcoming meeting, the plan is to ensure Russia's support for Annan's peace plan for the politico-democratic regulation of the crisis in Syria.

"It is the Russian side's understanding that this plan is the only viable platform to the solution of Syria's internal problems."