Sudan - Northern and southern Sudan have signed a deal aimed at bolstering a fragile peace accord they signed in 2005, in front of the US envoy to the country.

Scott Gration said the deal, which agrees how to take Sudan to next year's election, heralded a "brighter future".

But he gave few details, and analysts say it is more of a commitment to work together than a substantial deal.

The two sides were at war for 22 years and have blamed each other for a recent series of deadly clashes.

A journalist in South Sudan's capital, Juba, says people are in optimistic mood and are hopeful that the politicians will carry through their promises.

But he says there are several issues that need to be sorted out - not least a referendum which will ask people in South Sudan if they want independence from the north.

The vote is scheduled for 2011, but the exact details have already sparked controversy - with officials from the south threatening to declare unilateral independence if they believe the poll will be unfair.

However, Mr Gration said the new deal engendered a "sense of co-operation" which was "a precursor of good things to come".

"It will result in better co-operation and stronger relations that will result in a brighter future for Sudan, for Khartoum and Juba," he told journalists after the deal was signed.

There has been increasing tension between the former enemies, with critics saying that time is running out for the 2005 peace deal.

Several hundred people have died in ethnic clashes this year and each side has blamed the other for causing the violence.

The two sides fought a 22-year brutal civil war over religious, ethnic and ideological differences in which an estimated 1.5 million people have been killed.

Under the 2005 peace deal the former rebel Sudan People's Liberation Movement formed a power-sharing government with President Omar al-Bashir's National Congress Party in Khartoum.

  A national election is due in 2010.