Shocking satellite images of destroyed towns and razed houses have confirmed eyewitness accounts that Boko Haram slaughtered hundreds of people this month in its worst-ever massacre in Nigeria, human rights groups say.

The wave of savage attacks continued relentlessly for several days after Boko Haram captured the Baga military base on Jan. 3. The Nigerian military has insisted that only 150 people died, including militants, but the newly released satellite images suggest a far more horrifying toll.

The images show more than 3,700 damaged or destroyed houses in just two of the estimated 16 towns and fishing villages that the Islamist extremist militia attacked around Baga in northeastern Nigeria on the shores of Lake Chad, according to Amnesty International, one of the groups that released the satellite images.

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"These detailed images show devastation of catastrophic proportions in two towns, one of which was almost wiped off the map in the space of four days," said a statement on Thursday by Daniel Eyre, a Nigeria researcher for Amnesty International.

Mr. Eyre described it as the "largest and most destructive" of all of the Boko Haram atrocities that Amnesty has ever analyzed since the militia began its rebellion in 2009.

Some reports, citing local officials and human rights researchers, have suggested that as many as 2,000 people were killed.

Based on interviews with eyewitnesses, as well as local government officials and human rights activists, Amnesty has concluded that Boko Haram "shot hundreds of civilians." A further 20,000 people have fled to Chad, Cameroon and Niger in the past two weeks to escape Boko Haram, including about 2,000 who are stranded on islands in Lake Chad.

Even small children and women were brutally killed in the attacks. Among them were a pregnant woman who was in labour and her partially born child, Amnesty said. One survivor told Amnesty: "There were bodies everywhere we looked."

Another group, Human Rights Watch, conducted its own analysis of the satellite images and described them as "direct evidence" of a "systematic campaign of arson directed against the civilian population in the area."

It estimated that "several thousand" buildings were destroyed by deliberate fires in the town of Doro Gowon, near Baga, the site of an international military base. About 57 per cent of the town was destroyed, it said.

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Boko Haram has been escalating its attacks in northern Nigeria for years, and the Nigerian military has seemed helpless to stop the atrocities. After the Baga massacre, Boko Haram triggered deadly explosions in several towns by strapping bombs to the bodies of girls as young as 10, then detonating them when the girls were in crowded areas.

Last year, the radical Islamists provoked a global furor by kidnapping more than 200 schoolgirls from the town of Chibok in the same state where Baga is located. The military vowed to rescue the girls, but have proven unable to find them or free them.

With elections due on Feb. 14 in what is Africa's biggest economy and most populous country, the Boko Haram rebellion will cast serious doubt on the election results, since there is little chance of any free voting in the 50,000 square kilometres of territory that the militants control.

Many Nigerians were outraged that President Goodluck Jonathan said nothing about the Baga massacre, even while he was expressing his sympathy to France for the terrorist attacks in Paris last week. Across Africa, there was resentment that dozens of world leaders had journeyed to Paris for a solidarity march after the terrorist attacks, while those same leaders seemed to do nothing against Boko Haram, despite the much higher death toll in Nigeria. Countries such as South Africa criticized the apparent inaction.

The uproar led to loud rhetoric from the African Union this week. It demanded a "co-ordinated African and international response" against Boko Haram, including the mobilization of stronger support for an international military force in northeastern Nigeria, known as the Multinational Joint Task Force, which comprises troops from Nigeria, Chad and Niger.

But it was the task force's base near Baga that was overrun by Boko Haram this month, showing the weakness of its forces. Months earlier, Niger and Chad had withdrawn their troops from the base as Boko Haram moved closer. Nigerian media reports this week predicted that the collapse of the joint task force is "imminent."

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For months, the African Union has focused on the multinational task force as the best way of beating Boko Haram. If this doesn't work, it has few other options. The AU has been trying to establish its own rapid-reaction force of about 8,000 troops to respond to crises, but most of these troops would probably be South African and they simply aren't available for Nigeria now. Many of the South African troops are already occupied by United Nations military operations in the Democratic Republic of the Congo.

If African forces are unable to help Nigeria, it is unlikely that others will arrive. The United States, Canada and European countries are reluctant to send military aid to the Nigerian Army because of widespread concerns about its corruption and human rights abuses.