The airspace over most of Bosnia, Serbia and Montenegro and parts of air corridors over international waters in the Southern Adriatic has been closed to flights with effect from 1400 GMT on Saturday, Serbia's air traffic control said in a statement.
Belgrade airport will closed at least until 2300 GMT, the body's press office said.
Meanwhile, The Irish Aviation Authority said it had extended the closure of Irish airspace to commercial traffic until 1200 GMT on Sunday because of the volcanic ash cloud over Europe.
The airspace had initially shut down until 1700 GMT on Saturday.
Also, Most flights over Britain will remain grounded until at least 0600 GMT on Sunday because of the dangers posed by clouds of volcanic ash from Iceland, UK aviation officials said on Saturday.
The air traffic body NATS said some airspace might be available up to 1800 GMT within Scotland, Northern Ireland and northern England.
"(This) may enable some domestic flights to operate under individual coordination with air traffic control," it said.
NATS said it would continue to review weather information and would issue an update around 2000 GMT.
German airspace will remain closed until 600 GMT on Sunday because of the volcanic ash cloud over Europe, a spokeswoman for the country's air traffic control body said on Saturday.
Previously, the organisation had said German airspace would be shut until 2400 GMT on Saturday.
ReutersLast Mod: 18 Nisan 2010, 13:12