The United States will have to keep up an open-ended drone war against al-Qaida militants in Pakistan and elsewhere to prevent another terror attack on America, Defense Secretary Leon Panetta said.

The assassination of al-Qaida figures in Pakistan, Yemen and Somalia with unmanned, robotic aircraft has provoked widespread criticism from human rights groups and some U.S. allies, but Panetta said the U.S. campaign has been effective.

Amnesty International on Friday called on the French army to launch an independent investigation into the deaths of five civilians killed in a helicopter attack at the start of the Mali campaign.

A report from the London-based rights group also highlighted summary executions by Malian troops and Islamist groups, as well as the Islamists' use of child soldiers.

President Francois Hollande prepared to visit Mali as French-led troops worked Friday to secure the last Islamist stronghold in the north after a lightning offensive against the extremists.

Hollande will visit Mali on Saturday with Defense Minister Jean-Yves Le Drian and Development Minister Pascal Canin, his office said, three weeks after French troops launched a surprise intervention against Islamists in its former colony.

A Malian military spokesman said on Thursday that four soldiers died and five others were wounded when their vehicle hit a land mine in eastern Mali.

Modibo Traore told The Associated Press that the soldiers were killed Wednesday evening in the town of Gossi.

The U.N. cultural organization UNESCO on Wednesday said it would send a mission to the historic city of Timbuktu in war-torn Mali as soon as possible to assess the damage done to ancient cultural sites.

"UNESCO will send a mission, as soon as security permits, to undertake a complete evaluation of the damage and determine the most urgent needs, in order to finalize a plan of action... that will guide reconstruction and rehabilitation," the body's director general Irina Bokova said in a statement.

British Prime Minister David Cameron arrived in Algeria on Wednesday in the wake of this month's hostage crisis at a gas plant deep in the Sahara in which several Britons were killed.

The first visit by a British premier since Algeria won independence from France in 1962 comes less than two weeks after 37 foreign hostages were killed when Islamists stormed the In Amenas facility and in the attack's aftermath.

South African President Jacob Zuma claimed the war in Mali was a consequence of Western powers forcing the overthrow of Libyan leader Moammar Gadhafi, in a radio interview broadcast Wednesday.

Describing the situation in Mali as "quite grave" Zuma told Paris-based RFI that "it is important to look at Mali as a consequence of how we handled Libya".

France on Wednesday urged the Malian government to quickly enter into peace talks with Tuareg rebels and other representatives of the population in the north of its former colony.

The call came after a French-led military campaign ousted Islamist groups from the major towns of Mali's desert north, which they had controlled since last April.

French troops on Wednesday entered Kidal, the last Islamist bastion in Mali's north to be recaptured in a whirlwind Paris-led offensive amid reports the radicals have regrouped in remote hills near Algeria.

Their arrival in Kidal comes days after the capture of Gao and Timbuktu in a three-week offensive that Paris now hopes to wind down and hand over to African troops.

Hundreds of Malians from the rebel-held northern town of Kidal have fled towards the Algerian border, the U.N.'s refugee agency said Tuesday, adding that some had even crossed the officially closed frontier.

Residents had fled the town "to villages further north, even closer to the Algerian border," UNHCR spokesman Adrian Edwards told reporters in Geneva. "Others have crossed the border into Algeria."