United Nations chief Ban Ki-moon says he is “deeply concerned” over the lack of disarmament of the militant and political group Hezbollah.

Mr. Ban is in Lebanon for talks on a U.N.-backed tribunal probing the death of the country's former leader and the ongoing bloodshed in neighboring Syria.

At a press conference Friday not far from Hezbollah's Beirut base, Mr. Ban said he encouraged Lebanese leaders to “support and cooperate fully” with the tribunal investigation of the 2005 assassination of former Prime Minister Rafik Hariri.

Four members of Hezbollah have been accused in the bombing that killed Mr. Hariri and 22 others in the Lebanese capital. Mr. Ban said he hopes the U.N. body will renew the tribunal's mandate that is due to expire at the end of February.

Ahead of Mr. Ban's arrival, a Hezbollah official made clear that the U.N. chief is not welcome in Beirut.

Hezbollah, Lebanon's strongest political faction, has denied involvement in the slaying and has refused to hand over the four suspects to the Special Tribunal for Lebanon.

Mr. Ban has repeatedly called for Hezbollah to disarm. Hezbollah is the only Lebanese faction that has refused to lay down its arms following the 1975-1990 civil war.

The U.N. secretary-general also was expected to discuss recent attacks against U.N. peacekeepers in southern Lebanon with Lebanese leaders, including President Michel Suleiman, Prime Minister Najib Mikati and officials of parliament.