The UN Security Council met in emergency session to discuss the escalation of violence in Georgia's separatist region of South Ossetia, dpa reported.
Russia, which is closely allied with South Ossetia, called the meeting, which began late Thursday in New York. Its ambassador, Vitaly Churkin, accused Georgia of aggressive behaviour toward the breakaway region.
While the meeting was taking place, the Georgian government and South Ossetia separatists deployed fighter jets to carry out bombings on one another Friday after a ceasefire declared by Georgian President Mikheil Saakashvili was broken after a few hours, a news report said.
Many civilians were killed in the airstrikes, Russia's Interfax news agency reported, citing South Ossetia's Health Ministry.
The South Ossetia side for the first time deployed two Suchoi SU-25 fighter jets to bomb Georgian positions, and a short time later, Georgia sent five of the same jets to carry out attacks in South Ossetia, Interfax said.
Unconfirmed reports said at least 15 people, primarily civilians, were killed in the South Ossetia capital of Tskhinvali alone.
Abkhazia, another separatist region of Georgia, offered military aid to South Ossetia while Russia called for both sides to act rationally.
Television footage showed heavy rocket bombardments in the small mountain region in the South Caucasus.
The Georgian government accused South Ossetia fighters of breaking the ceasefire overnight, Russia's Itar-Tass news agency said.
South Ossetia separatists resumed shooting at Georgian villages late Thursday, causing deaths and injuries, the government in Tbilisi said in a statement carried by the agency.
It said it was forced to take steps to protect the people in the region and prevent further gunfire. At the same time, it called on the South Ossetia side to halt the fighting, which began at the weekend, and return to negotiations.
Both South Ossetia and Abkhazia fought wars of independence against Tbilisi in the early 1990s but have not been recognized by any other country. Since 1994, they have been occupied under a UN deal by peacekeepers from Russia.
UN Secretary General Ban Ki-moon expressed concern about the latest fighting in a statement issued Thursday in New York and urged warring parties to refrain from action that could endanger stability in their region.