A U.S. military Reaper drone crashed in Mali in April as it was carrying out a surveillance flight over the troubled west African nation, a U.S. defense official said Friday.

The robotic, unmanned aircraft went down due to "mechanical failure," the official, who spoke on condition of anonymity, told Agence France Presse.

The U.N. envoy to the Sahel region on Wednesday warned of a difficult election campaign ahead in Mali, pointing in particular to the problem of ensuring refugees could vote and the need to improve security.

Romano Prodi, a former European Commission president and former Italian prime minister, also said there had been no "definitive" conclusion to the military conflict since arms were still widely available.

Mali's army has accused a Tuareg rebel group of breaching a peace accord in the flashpoint northeastern town of Kidal, by attacking civilians and soldiers.

"The MNLA has mobilized women and children in Kidal to throw stones at the black population, African (peacekeeping) troops and Malian soldiers," army spokesman Lieutenant-Colonel Diarran Kone said late on Sunday, referring to the Tuareg separatist National Movement for the Liberation of Azawad (MNLA).

Mali lifted a five-month state of emergency on Saturday, the eve of the start of a presidential election campaign for July 28 polls in the troubled west African nation, the security ministry said.

The state of emergency was put in place on January 12, a day after France launched a surprise intervention to help Mali's weak army drive out Islamists occupying its north for nine months.

Mali's elections will go ahead as planned on July 28, the government said on Tuesday, amid doubts over the conflict-scarred nation's ability to organize a free and fair nationwide vote in just four weeks.

The caretaker government announced presidential elections just over a month ago, raising urgent questions over the possibility of inclusive polls in a nation recovering from a coup that paved the way for Islamist rebels to seize control of the north.

United Nations peacekeepers took over security duties from African troops in Mali on Monday with a mission to ensure stability in the conflict-scarred nation just four weeks ahead of planned elections.

A 12,600-strong force officially replaced the AFISMA military mission, which has been supporting French soldiers who entered Mali in January to halt an Islamist advance and to help the government re-establish its authority over the vast country.

United Nations soldiers will take over from African troops in conflict-scarred Mali from Monday, making up the organization’s third-largest peacekeeping force by the end of the year.

A 12,600-strong force will take over security duties from French troops who entered Mali in January to halt an Islamist advance and help the government re-establish its authority over the vast country.

The European Commission on Tuesday made a first payment of 90 million euros ($118 million) to Mali, as part of an aid package to bolster the troubled country and recognize democratic progress.

The money is part of a 523-million-euro package announced by the Commission at a donor conference last month and comes ahead of Mali's presidential election set for July 28.

A U.N. peacekeeping force will take charge of security in Mali from July 1 but plans to hold a presidential election next month face "major" obstacles, officials said Tuesday.

The United Nations also is worried about Mali's furnace-like temperatures melting equipment as it confronts one of its biggest logistical challenges in setting up the 12,600 strong force, which already faces key shortages.

Around 700 EU-trained soldiers have been deployed to war-torn Mali's desert north, a military source told Agence France Presse on Tuesday.

The contingent -- the first from the European Union Training Mission in Mali -- left the capital Bamako on Monday for the northeastern city of Gao, a Malian defense ministry official said on condition of anonymity.