A new Boko Haram massacre has killed hundreds in Nigeria's northeast, a senator said Wednesday, as police offered $300,000 dollars for information leading to the rescue of more than 200 schoolgirls held hostage by the Islamists. The latest insurgent attack targeted the town of Gamboru Ngala on the border with Cameroon, where gunmen this week razed scores of buildings and fired on civilians as they tried to flee. Area Senator Ahmed Zanna put the death toll at 300, citing information provided by locals, in an account supported by numerous residents. Zanna said the town had been left unguarded because the soldiers based there had been redeployed north towards Lake Chad in an effort to rescue more than 200 girls kidnapped by Boko Haram on April 14. The shocking mass abduction has sparked global outrage and offers of help from the United States, Britain, France and China. Nigeria's response to the kidnappings has been widely criticised, including by activists and parents of the hostages who say the military's search operation has been inept so far. The police on Monday offered 50 million naira ($300,000, 215,000 euros) for any information leading to the girls' rescue. President Goodluck Jonathan's administration has sought to appear more engaged with the plight of the hostages in recent days, especially after Boko Haram chief Abubakar Shekau released a video threatening to sell the girls as "slaves." In a second kidnapping, eleven more girls aged 12 to 15 years were seized Sunday from Gwoza, an area not far from Chibok and also in Borno state, Boko Haram's base. The group's five-year uprising has killed thousands across Africa's most populous country and top economy, with many questioning whether Nigeria has the capacity to contain the violence. - Town 'completely burnt' - Islamist fighters riding in armoured trucks and on motorcycles stormed Gamboru Ngala after midday on Monday. Survivors said the extremists overran the town making it too dangerous for locals to immediately return. When the Islamists left, residents went back to a town that was "littered" with dead bodies, Musa Abba, a witness, told AFP. "All economic and business centres have been burnt. The market in the town which attracts traders from all over the area... has been completely burnt," the senator said. Gamboru Ngala has been attacked repeatedly in the past, but Abba said "this (was) the worst Boko Haram attack (the town) has seen." - West joins hostage search - US President Barack Obama has described the Chibok abductions as "heartbreaking" and "outrageous", and announced that a team of military experts had been sent to help Nigeria's rescue mission. British Prime Minister David Cameron on Wednesday condemned the kidnappers as "pure evil" as his office said Britain was sending a team of experts to help with the kidnap response. French Foreign Minister Laurent Fabius said a "special team" was at Nigeria's disposal, while Jonathan said that visiting Chinese Premier Li Keqiang has also pledged assistance. Analysts said Jonathan's acceptance of Western military assistance suggested an admission he can no longer manage the Boko Haram uprising without help. As well as mounting pressure over the kidnappings, Nigeria has been hit by a spate of bombings. Just a few hours before the mass abduction in Chibok, a blast ripped through a crowded bus station on the outskirts of Abuja, killing 75 people in the deadliest attack to hit the capital. A copycat bombing at the same station killed 19 people on May 1. To contain the violence, Jonathan has imposed a state of emergency in Boko Haram's northeast stronghold where he sent thousands of troops to flush out the insurgents, but critics say the offensive has achieved almost nothing. Efforts by prominent northern leaders to negotiate a ceasefire have been publicly rejected by Shekau. - World meet overshadowed - Jonathan had hoped that a World Economic Forum summit which opens in Abuja on Wednesday would highlight Nigeria's economic progress and underline its recent emergence as Africa's biggest economy. Meeting Jonathan in Abuja ahead of the summit, China's Li pledged stronger cooperation with Nigeria, Africa's top oil producer, but public focus has remained fixed on Boko Haram. Amid the outrage over the kidnappings and the twin attack just a few kilometres from central Abuja, Nigeria has promised the World Economic Forum will be kept safe by the 6,000 troops deployed across the capital. "That show of force may keep the delegates safe, but Nigeria's deeply troubled government cannot protect its people, attract investment and lead the country to its full potential if it cannot contain a virulent insurgency," the New York Times said in an editorial on Wednesday.