310 people killed in latest Boko Haram attack while hundreds of girls remain missing

Abuja, Nigeria (CNN) -- As the world fumes over Boko Haram's kidnapping of hundreds of girls, the terror group's latest attack in northern Nigeria has left 310 people dead, residents said.

The world still doesn't know what happened to the 276 girls kidnapped almost a month ago, except that Boko Haram's leader said he plans to sell them.

Now, the militants may be going after those trying to find the girls.

The latest attack took place in the town of Gamboru Ngala. Troops had been using the area as a base in the search, witnesses told CNN Wednesday. Some of the victims were burned alive.

Word of the attack Monday came after President Goodluck Jonathan accepted U.S., British and Chinese offers of assistance to find the schoolgirls, officials from those governments said.

It's unclear what impact the latest attack could have on the international response to Nigeria's fight with Boko Haram.

Even as several countries ratchet up their support in finding the girls, the inability to find them so far has been unnerving.

"Every day when I wake up and I think about young girls in Nigeria or children caught up in the conflict in Syria, when there are times in which I want to reach out and save those kids, and having to think through what levers, what powers do we have at any given moment," U.S. President Barack Obama said Wednesday night in Los Angeles.

"I think drop by drop by drop that we can erode and wear down these forces that are so destructive."

Exactly how remains a mystery.

The latest assault

Witnesses described a well-coordinated attack that began shortly after 1:30 p.m. local time Monday at a busy outdoor market in Gamboru Ngala.

Wearing military uniforms, the militants arrived with three armored personnel carriers, they said.

They shouted "Allahu Akbar" -- "God is great" -- and opened up on the market, firing rocket-propelled grenades and tossing improvised explosive devices, witnesses said.

Some marketgoers tried to take shelter in shops only to be burned alive when the gunmen set fire to a number of the businesses, the witnesses said.

A few Nigerian soldiers who had been left behind at the village could not hold off the assault and were forced to flee, they said. Many sought safe haven in nearby Cameroon, they said.

The fighters also attacked the police station during the 12-hour assault, initially facing stiff resistance. They eventually used explosives to blow the roof off the building, witnesses said. They said 14 police officers were found dead inside.

The final death toll could be closer to 300, Nigerian Sen. Ahmed Zanna told CNN.

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Monday's bloody attack by Boko Haram militants, some of whom U.S. officials say have been trained by al Qaeda, follows a pattern of revenge-seeking against anybody perceived to have provided aid to the Nigerian government.

International effort

Nigerian police announced a 50 million naira ($319,000) cash reward for information leading to the rescue of the 276 girls kidnapped from the Government Girls Secondary School in Chibok. The announcement came after Nigeria's government came under harsh criticism for its response.

The girls from Chibok aren't alone. At least eight girls between the ages of 12 and 15 were snatched Sunday night from the village of Warabe by Boko Haram, villagers said.

The Pentagon has started planning for how it can help Nigeria, a senior U.S. military official told CNN. It's unlikely at this point that U.S. troops would be involved in operations, the officials said.

Britain is sending a small team of experts to complement the U.S. team, a spokesman for Prime Minister David Cameron said Wednesday, but the spokesman didn't specify the nature of the team's expertise.

And Chinese Premier Li Keqiang offered satellite and intelligence services to aid in the search.

'I will sell women'

The increased global response to the April 14 abductions came after a chilling video described what may happen to the girls.

A man claiming to be Boko Haram's leader, Abubakar Shekau made the following claim:

"I abducted your girls. I will sell them in the market, by Allah," he said. "There is a market for selling humans. Allah says I should sell. He commands me to sell. I will sell women. I sell women."

Boko Haram translates to "Western education is sin" in the local Hausa language. The group has said it wants a stricter enforcement of Sharia law across Africa's most populous nation, which is split between a majority Muslim north and a mostly Christian south.

The militants have even been known to kill Muslim clerics who dare criticize them.

The United States has branded Boko Haram a terror organization and has put a $7 million bounty on Shekau. But his location is as uncertain as the whereabouts of the girls.