The International Committee of the Red Cross (ICRC) yesterday said that it considered Ukraine to be in a state of civil war, urging both sides to respect the laws of conflict as civilians bear the brunt.
The formal classification means participants in the fighting between government forces and pro-Russian separatists in the east could eventually be prosecuted for war crimes in international courts.
"Fighting in eastern Ukraine continues to take its toll on civilians, and we urge all sides to comply with international humanitarian law, otherwise known as the law of armed conflict," ICRC director of operations Dominik Stillhart said in a statement.
"These rules and principles apply to all parties to the non-international armed conflict in Ukraine, and impose restrictions on the means and methods of warfare that they may use," he added.
The Swiss-based humanitarian body is the watchdog for the Geneva Conventions, the rules governing conduct in conflict. The Red Cross uses the term "non-international armed conflict" for civil war.
It came as Pro-Russian rebels yesterday shot down two Ukrainian fighter jets in the insurgent-held area where Malaysia Airlines flight MH17 was downed.
"Terrorists have shot down two Ukrainian Su-25 jets," the press office for Kiev's military campaign against the insurgents said in a statement.
The planes were hit by missiles fired by rebels close to the village of Dmytrivka, some 45 kilometres south-east of the MH17 crash site towards the Russian border, as they were providing air support for government infantry, the statement said.
The pilots from both jets managed to parachute out, it said, giving no further details about their condition. A spokesman for the self-proclaimed Donetsk People's Republic told AFP its fighters had shot down the two aircraft.
The downing of the government jets comes just six days after the insurgents were accused of shooting down the Malaysian passenger plane using a surface-to-air missile, killing all 298 people on board.
The rebels have denied that they downed flight MH17, accusing the Ukrainian military of being responsible for hitting the jet.
Russia starts reinforcing naval fleet in Crimea
Russia yesterday announced that it had begun expanding and modernising its Black Sea fleet based in Crimea with new ships and submarines, just months after annexing the peninsula from Ukraine.
"Today we have started forming a powerful Black Sea fleet with an absolutely different level of air service, coastal missile and artillery troops and marines," said Alexander Vitko, the Black Sea fleet commander, in a message to servicemen.
Vitko said the modernisation of the fleet "lays the foundation for the future of the fleet, both in the short term and looking far ahead."