The Red Cross had previously designated Idlib, Homs and Hama as war zones, but the change in status means international humanitarian law applies wherever fighting occurs throughout the country

Combatants will now be officially subject to the Geneva Conventions, and will be more exposed to war crimes prosecutions, after the ICRC declared that the conflict was a "non-international armed conflict", or in lay terms a civil war.

Sean Maguire, a spokesman for the ICRC, said that both sides would be reminded of their obligations "to protect civilians from fighting, treat the wounded and sick without discrimination".

The categorisation was made after the ICRC determined that the armed opposition to Bashar al-Assad's regime had reached a sufficient level of organisation and capability.

The Syrian Observatory for Human Rights reported heavy clashes in the capital in what was described as the "most intense" fighting there since the start of the anti-regime revolt in Syria.