West African leaders gathered for emergency talks Friday on the crisis in Ivory Coast with the United States searching for more UN troops and France offering Laurent Gbagbo a final chance to step aside.

The summit comes after a UN body demanded a halt to "atrocities" in Ivory Coast and the Central Bank of West African States blocked Gbagbo's access to finances, putting a further squeeze on his bid to remain in power.

Much of the world, including the United Nations, has recognised Gbagbo's rival Alassane Ouattara as the winner of last month's elections, but the strongman has refused to budge in the face of mounting calls for him to leave.

As leaders arrived for the ECOWAS summit, Nigeria's foreign minister sought to keep the pressure on Gbagbo, saying there would be no compromise on the bloc's demand that he step down.

"The question of compromise is not on the table," Odein Ajumogobia told AFP ahead of the special summit of the 15-member Economic Community of West African States.

"Something like a unity government or the sort of thing we have in Kenya and Zimbabwe are not on the table. We are resolute that Gbagbo has to step down."

The meeting of West African leaders will be their second special summit on Ivory Coast this month after having suspended the country from the group at the first gathering and called on Gbagbo to cede power.

Some analysts have said the bloc could impose individual sanctions such as travel restrictions over the crisis, but officials have been tight-lipped over what will be on the table at the summit in the Nigerian capital Abuja.

The United States has also said it is talking with regional countries from ECOWAS about boosting the 9,000-strong UN mission in Ivory Coast.

French Foreign Minister Michele Alliot-Marie said Friday that Gbagbo could still step down honourably, but warned that time was growing short.

"Mr Gbagbo still has the possibility of leaving this situation with dignity by recognising what the results are and by handing over power," she told French radio.

"He has the right to a completely honourable exit... but the more time passes and the more things get out of control and there's violence, the more this possibility distances itself."

Both US President Barack Obama and French President Nicolas Sarkozy have spoken by phone on the crisis to their Nigerian counterpart Goodluck Jonathan, who is the current ECOWAS chairman.

Jonathan has also sent Gbagbo a letter on behalf of ECOWAS calling on him to yield power immediately and offering to help him and his family resettle.

On Thursday, the UN Human Rights Council passed by consensus a resolution strongly condemning abductions and killings in Ivory Coast's post-election violence and expressing concern about "atrocities".

The move at a special session on the Ivorian crisis called by Nigeria on behalf of African states and the United States marked a rare display of unity by the world body's Geneva-based rights assembly.

The vote came after a senior UN rights official told the council that her staff had gathered credible reports of at least 173 killed over the past week in Ivory Coast as well as allegations of mass graves.

A senior UN official was stopped at gunpoint as he sought to verify the allegations in the west African country, UN Deputy High Commissioner for Human Rights Kyung-wha Kang said.

One analyst said targeted sanctions may be the likely path for ECOWAS for now.

"A travel ban is a strong possibility except for travel related to mediation," said Alex Vines, head of the Africa programme for London-based think tank Chatham House and a former UN sanctions inspector.

"I think ECOWAS might also signal they might support UNOCI further if requested by the UN and things get worse," he added, referring to the UN mission in the country.

Gbagbo and long-time rival Ouattara have been locked in a standoff since the November 28 presidential election, which both claim to have won. UN chief Ban Ki-moon has voiced fears of a return to civil war.

burs-mjs/co