UN chief Ban Ki-moon was set on Wednesday to announce a UN probe into the assassination of former Pakistani premier Benazir Bhutto during a flying visit to Islamabad, the foreign ministry said.
Ban's visit here, his first since taking office two years ago, after a stopover in Afghanistan comes two days after unidentified gunmen kidnapped a top UN official in southwest Pakistan two days ago.
It also comes amid rampant unrest in Pakistan's border areas, with Taliban rebels disrupting a crucial NATO supply route into Afghanistan and government forces engaged in bloody fighting in the northwest Swat valley.
The foreign ministry says Ban's talks will focus on the expected formation of a UN commission to investigate the December 2007 assassination of Bhutto, a two-time prime minister who was killed at a campaign rally.
"He's arriving in the afternoon. He will meet Prime Minister Yousuf Raza Gilani. Then he will call on President Asif Ali Zardari and attend a banquet before leaving for India tonight," a foreign ministry official told AFP.
"He is expected to announce the formation of a commission to investigate Benazir's killing," the official added.
Bhutto, the first woman to become prime minister of a Muslim country, was killed on December 27, 2007 in a gun and suicide attack after addressing an election rally in Rawalpindi, a garrison city near the capital Islamabad.
The Pakistani government and US officials accused tribal warlord Baitullah Mehsud of plotting the attack, although he denies the charge.
Pakistan asked the United Nations to establish a commission to investigate the slaying.
In December, a spokesman for Ban said that the UN leader hoped a commission could be established soon but further consultation with Pakistan was needed to examine its structure, "including its scope and mandate."
The UN secretary general has called for the "immediate and safe release" of John Solecki, the head of the UN refugee agency (UNHCR) in the city of Quetta who was snatched at gunpoint on Monday.
Pakistan condemned the "dastardly terrorist act" and launched a manhunt to find Solecki, but officials say they have no idea who was responsible.
Criminal gangs, rebels and Islamist militants are known to operate in the area.
Ban is also expected to discuss various regional and international issues, including the situation in Afghanistan and the Mumbai attacks in November last year, the foreign office said.
New Delhi blamed the attacks in Mumbai, which left 165 people dead. on the banned militant group Lashkar-e-Taiba which is active in Indian-ruled Kashmir, but the Pakistan-based organisation has denied responsibility.
Pakistan says the lone surviving Mumbai gunman, now in Indian custody, is a Pakistani citizen but has insisted the attackers were "non-state actors."
In a related issue, Ban is expected to discuss the implementation of a UN Security Council sanctions committee statement targetting four members of LeT and a charity Jamaat-ud-Dawa, widely viewed as its political arm.
Vowing to "fulfil its international obligations," Pakistan detained scores of Dawa officials and ordered its assets frozen after the UN Security Council in December moved to list the charity as a terror group.
The 60-hour siege in India's financial capital in late November has badly strained relations between nuclear-armed neighbours India and Pakistan.