NAIROBI -- Sudan's vice-president resumed talks with the leader of the main rebel group on Sunday to try to breathe life into stalled peace talks, officials said.

"They have decided to go back to one-on-one talks to try to break the impasse," said a source close to the negotiations aimed at ending Sudan's 20-year civil war.

Talks between First Vice-President Ali Osman Mohamed and John Garang, the head of the Sudan People's Liberation Army (SPLA), had started on Thursday.

Both sides have said the talks were critical to the peace process. Mediators said last month the government and rebels were under intense pressure by regional leaders to strike a deal, Reuters reported.

Peace talks have stumbled in recent months after reaching a breakthrough outline accord just over a year ago. The next round of the formal peace talks is due to start on September 10.

The war in Sudan broke out in 1983 and pits the Islamist government in the north against rebels seeking more autonomy in the south, where Christianity and animist beliefs dominate.

Officials say the major issues of disagreement are how to carve up power and wealth especially oil. Other problems include security and three areas of conflict -- Abyei, the Nuba Mountains and Southern Nile, claimed by both sides.

Sudan's Army said on Saturday it was committed to a separate truce with rebels in the country's western Darfur region.