UN Secretary-General Ban Ki-moon Thursday expressed his concern over the deteriorating situation in Sri Lanka and repeated his appeal to the Tamil rebels to lay down arms to end the nation's 25-year civil war.

"I am most concerned at the rapid deteriorating situation in Sri Lanka. I would like to take this opportunity to strongly urge all the parties concerned to respect the call of the Security Council I made yesterday, without further delay," Ban told reporters in Brussels following an international donor's conference for Somalia.