UN Secretary General Kofi Annan has spoken to President Pervez Musharraf over the phone to discuss the formation of a joint international force for the protection and security of the UN setup in Iraq.

United Nations' special envoy to Iraq Sergio Vieira de Mello was among 18 persons killed when a  powerful truck bomb exploded at the UN headquarters in Baghdad on Tuesday.

In his brief chat with Musharraf, Annan discussed the security of the UN staff, its officers and its aid programme, Pakistani news agency NNI quoted UN officials saying.

Besides Musharraf, Annan has had talks with several other world leaders.

"President Musharraf will discuss the contents of the discussion with Prime Minister Mir Zafarullah Khan Jamali," Pakistani officials said.

The issue of sending troops to Iraq has become a major problem for Musharraf as the six-party Islamic alliance Mutahida Majlis Amal is against Pakistan sending troops to Iraq.

For his part, Musharraf maintains that Pakistan would require a UN or Organisation of  Islamic Countries cover to send troops to Iraq.