Talks between Malian authorities and armed ethnic Tuareg rebels aimed at resolving the conflict in the north of the country opened on Saturday after a day's delay.

"The aim is to find a durable solution to the grave crisis engulfing Mali," said President Blaise Compaore of Burkina Faso which is mediating the negotiations.

Mali's army on Thursday reinforced its positions at Anefis, a strategic access point for the rebel-held town of Kidal, after a day of heavy fighting, military sources said.

"We are reinforcing and consolidating our positions at Anefis while waiting for favorable conditions to pursue the operation" towards Kidal in the northeast, army spokesman Lieutenant-Colonel Souleymane Maiga told Agence France Presse.

Malian soldiers clashed with Tuareg separatists from the National Movement for the Liberation of Azawad Wednesday in a town south of the rebel-held regional capital of Kidal, military sources told Agence France Presse.

Troops attacked militant positions in Anefis, 200 kilometers (125 miles) south of Kidal, as part of an operation to retake the city from the ethnic Tuareg MNLA which is accused of "ethnic cleansing" after a wave of expulsions of black residents.

A suicide bomber blew himself up Tuesday at the house of a Tuareg military leader in the northern Malian city of Kidal, witnesses and a military source said.

"The suicide bomber was waiting for someone in the (MNLA) colonel's house when he was caught by some youths and set off his bomb. He is dead and there is one person wounded," the military source told Agence France Presse.

The United Nations is struggling to get African troops in Mali up to U.N. standards to join a full-fledged peacekeeping force, a top U.N. official said Wednesday.

U.N. peacekeeping chief Herve Ladsous said it would be a "big challenge" for West African contingents to meet U.N. norms. But he expressed confidence that a U.N. force would start on July 1 and take over from French forces who are battling violent extremists.

Mali's main political parties welcomed the announcement of July 28 presidential elections in a rare show of unity Tuesday in the deeply-divided and battle-scarred west African nation.

The country's interim cabinet on Monday officially confirmed for the first time the date of the poll, seen as essential to restoring democracy after a coup last year paved the way for Islamist rebels to seize control of the north.

The jihadist group led by Algerian Mokhtar Belmokhtar that claimed twin suicide car bombings in Niger that killed at least 20 people threatened on Friday to launch further attacks in the country.

"We will launch further operations" in Niger, the group said in a statement posted on Islamist Internet forums that also threatened France and countries involved militarily in battling Islamist extremists in Mali.

China has offered to send more than 500 soldiers to the U.N. force seeking to contain Islamist militants in Mali in what would be its biggest contribution to U.N. peacekeeping, diplomats said.

The move could be a bid to overcome tensions with the West over the Syria conflict and to strengthen Beijing's relations in Africa, where it is a major buyer of oil and other resources, diplomats and experts said.

Mali's main Tuareg separatist group said Wednesday it supported the holding of a nationwide presidential poll in July but ruled out allowing the army in its northern bastion of Kidal for the vote.

A delegation from the National Movement for the Liberation of Azawad (MNLA) held talks in Ouagadougou, the capital of neighboring Burkina Faso, with the region's lead mediator in the Malian crisis, Djibrill Bassole.

A senior operative in an al-Qaida-linked group in war-torn northern Mali has surrendered to Mauritania, a security source told Agence France Presse on Monday.

Ansar Dine spokesman Senda Ould Boumama "went to the Mauritanian armed forces on the border", near the southeastern town of Bassiknou, on Saturday evening, the source said without giving further details.