Syrian police have killed two protesters after opening fire on a crowd who came to welcome United Nations observers in the east, according to a Free Syrian Army official.

"As soon as the UN convoy entered al-Busaira a jubilant crowd of hundreds came out to welcome them. It was not minutesbefore they came under fire," Abu Laila, a Free Syrian Army official, told the Reuters news agency by phone from the eastern province of Deir al-Zor.