Francois Fall, UN chief Kofi Annan's special representative for Somalia, will travel to Baidoa, the seat of the transitional government, on Monday for talks with Somali President Abdullahi Yusuf Ahmed, it said.
They will discuss "the current situation in Somalia and the way to preserve peace, security and unity," the Nairobi-based UN Political Office for Somalia said in a statement released in the Kenyan capital.
It did not say whether Fall would meet with Islamist officials.
The trip follows the emergence of an alarming report by UN experts of a massive military build-up in Somalia, fuelled by ten foreign nations and the radical Lebanese Hizbullah movement, most of whom support the Islamists.
Fall will be accompanied by members of the US-inspired International Contact Group on Somalia as well as African Union and Arab League envoys who have been trying to bring the government and Islamists together for peace talks, it said.
"The talks which are now suspended should resume very quickly," the statement quoted Annan as saying this week and calling on the two sides "to avoid further confrontation and military action."
Two rounds of peace talks were held in the Sudanese capital of Khartoum in June and September but a third round collapsed earlier this month, amid soaring tension and reports of widespread outside intervention.
The Islamists refuse to attend the talks until Ethiopia withdraws troops it has sent to Somalia protect Yusuf's government.
The sides are now girding for battle outside of Baidoa, about 250 kilometres (155 miles) north-west of Mogadishu and fears are running high for a full-scale war that could engulf the entire Horn of African region in conflict.
The Islamists seized Mogadishu from US-backed warlords in June and have since used the city as a base to take most of southern and central Somalia where they have imposed strict Sharia law.
The internationally backed government controls only Baidoa but is allied with authorities in the semi-autonomous north-eastern enclave of Puntland on which the Islamists are advancing.
The report compiled by experts monitoring a 1992 UN arms embargo paints an grim picture of foreign and extremist intervention in a nation on the brink of a full-scale war with major regional implications.
Due to be discussed by the UN Security Council on Friday, it says the current situation contains "all of the ingredients for the increasing possibility of a violent, widespread, and protracted military conflict."
"Moreover, there is the distinct possibility that (it) may spill over into a direct state-to-state conflict between Ethiopia and Eritrea, as well as acts of terrorism in other vulnerable states of the region," it says.
Arch-foes Ethiopia and Eritrea, still at odds over their own 1998-2000 border war, have thousands of combat troops in Somalia, according to the report.
Both countries deny this, although Ethiopia admits to sending military advisers to assist the government.
Backing the Islamists are Djibouti, Egypt, Eritrea, Iran, Libya, Saudi Arabia, Syria and Hizbullah, while Ethiopia, Uganda and Yemen are supporting the government, according to the report.
The Islamists have rejected the report as "entirely full of lies and fabrications of events" while nearly all the countries named have denied any involvement in Somalia.
The report details "rampant arms flows" of increasingly powerful and sophisticated weaponry, including shoulder-launched surface-to-air missiles and heavy arms, much of which are directed toward the Islamists.
Somalia has been without a functioning central authority since the 1991 ouster of dictator Mohamed Siad Barre.

Copyright AFP (Agence France-Presse), 2006