TRIPOLI, Libya, Feb. 21 -- The leaders of Sudan and Chad said they agreed Wednesday to redouble efforts to end violence spilling over their border from Darfur, scene of one of the world's worst humanitarian crises.

The accord was the only progress reported by officials at the end of a mini-summit of regional leaders that had also sought to widen rebel participation in a shaky peace for Darfur, where as many as 450,000 people have died since the conflict began in 2003.

Violence in the western Darfur region of Sudan has expanded into Chad, which accuses Sudan of supporting rebels launching cross-border attacks that have exacerbated ethnic tensions and triggered a flood of refugees.

Libyan leader Moammar Gaddafi has pressed Chad and Sudan to settle their differences as part of efforts to bring peace to Darfur, where 2.5 million people have been displaced since 2003.

The summit's other goal was to entice the National Redemption Front rebel coalition to meet Sudan's government to discuss joining a 2006 peace deal between Khartoum and a faction of the former rebel Sudan Liberation Movement. There was no word on whether such a meeting took place.

Meanwhile, the head of one of Darfur's main rebel groups said he is willing to call a cease-fire if Sudan stops attacks on civilians and agrees to renegotiate the peace deal -- but warned of a new offensive if it fails to do so. Khalil Ibrahim heads the Justice and Equality Movement, which along with most other rebel groups refused to sign on to the peace accord.