UN special envoy Olusegun Obasanjo on Sunday began talks with rebel leader Laurent Nkunda in the east of Democratic Republic of Congo, AFP reported.
The two men were meeting in the rebel-held territory of Jomba, 80 kilometres (50 miles) northeast of Goma, the provincial capital of Nord-Kivu.
Obasanjo arrived by helicopter from Goma, which lies near DR Congo's borders with Rwanda and Uganda, at 10:00 am (0800 GMT).
The two men shook hands warmly at the start of the meeting.
Nkunda, who was a general in the Congolese army before turning against the government, had changed out of his military uniform into a light grey suit with a white shirt and red tie. Obasanjo was in traditional Nigerian dress.
The former Nigerian president, who was also once a general, briefly inspected Nkunda's soldiers before the two men walked hand-in-hand into a small building to begin their talks.
The meeting took place as a UN official reported fresh fighting between Nkunda's National Congress for the Defence of the People (CNDP) 60 kilometres further north.
"Heavy fighting broke out around 7:00 am (0500 GMT)," said Lieutenant Colonel Jean-Paul Dietrich of MONUC, the UN mission in DR Congo.
"We have sent a substantial patrol with armoured vehicles," he added.
The clashes were taking place at the village of Ndeko, in the Rwindi district, 10 kilometres (six miles) southeast of the strategic town of Kanyabayonga in Nord-Kivu province.
Obasanjo's talks with Nkunda are particularly significant because none of the various foreign ministers and envoys who visited the country in recent weeks have officially met the rebel leader.
Obasanjo arrived in the country on Friday and has already met President Joseph Kabila and other senior officials, including ambassadors from countries that are members of the UN Security Council.
He flew into Goma on Saturday, as UN officials warned that the continued fighting was making the plight of an estimated 250,000 displaced people increasingly desperate.
Nkunda says he is defending local Tutsis against the Interahamwe, a Rwandan Hutu militia, some of whom have been implicated in the 1994 genocide of Tutsis and moderate Hutus in neighbouring Rwanda.
He has threatened to topple Kabila's government unless he is granted face-to-face negotiations but the president has so far ruled out any meeting.
Obasanjo, who was named as a special UN envoy to the Democratic Republic of Congo earlier November, was expected to give a press conference at 11:30 a:m in Goma.