Amid global outrage over the kidnapping of the teenagers, the United States, Britain and France are sending specialist teams to Nigeria.
China promised to supply “any useful information acquired by its satellites and intelligence services” to Nigeria.
The police on Wednesday offered $300,000 (215,000 euros) for information leading to the rescue of the girls.
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 soldiers based there had been redeployed north towards Lake Chad in an effort to rescue the kidnapped girls.
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.
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, 11 more girls aged 12 to 15 were seized Sunday from Gwoza, an area not far from Chibok and also in Boko Haram’s Borno 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.