Fighting has been so intense in parts of Syria that at times it has qualified as a localised civil war, the head of the International Committee of the Red Cross (ICRC) said on Tuesday.
Jakob Kellenberger said that conflict in Homs and the province of Idlib this year met the agency's three criteria of a non-international armed conflict - intensity, duration and the level of organisation of rebels fighting government forces.
"It can be a situation of internal armed conflict in certain areas: an example was the fighting in Baba Amro in Homs in February," Kellenberger told Reuters, making clear the criteria were not met in the entire country.
Andrew Clapham, director of the Geneva Academy of International Humanitarian Law and Human Rights, said the qualification could imply future prosecutions for war crimes.
"It is now clear that certain acts committed by either side in those places can qualify as war crimes," he told Reuters.
"It also means that the parties will be violating international humanitarian law if they attack civilians or civilian objects."
U.N. experts have compiled a list of Syrian figures suspected of crimes against humanity, but opposition from Russia and China means they are unlikely to appear in the dock at the international war crimes court soon.
The ICRC's lawyers and its aid workers in Syria have studied the question of civil war for much of the 14-month-old uprising, in which at least 9,000 people have been killed.
Only lately did they determine that Syrian rebels represent an "organised" opposition force. Kellenberger also noted that the nature of violence has shifted more to "guerrilla attacks".
In contrast, the ICRC was quick to describe last year's conflict in Libya as a civil war, once rebels had set up a headquarters and a command and control structure.
The ICRC assessment means that international humanitarian law, embodied in the Geneva Conventions laying down the rules of war, is applicable to both sides in some parts of Syria.
It requires the humane treatment of all people in enemy hands and the duty to care for the wounded and sick. But it also means that the parties to the internal conflict are entitled to attack military targets, under international humanitarian law.
[Reuters]