LAGOS, Nigeria — The Nigerian army says 335 Boko Haram extremists, including two top commanders, have laid down their arms and withdrawn from the sect in response to a military offensive in the northeast.

Military spokesperson Onyema Nwachukwu released photos on Monday of the men holding placards asking for forgiveness, and said the group's chief bomb expert and his deputy were among those who turned themselves in. Hundreds of women and children from the militants' families also surrendered.

There have been several reports of militants surrendering since the reported death of the group's leader Abubakar Shekau earlier this year.

It is, however, difficult to assess if the surrenders will be a major win for Nigerian forces fighting Boko Haram's decade-long insurgency, according to Sadeeq Shehu, a retired senior officer of the Nigerian Air Force.

Even before Shekau's death, he and his allies had faced a mounting threat from a breakaway faction known as the Islamic State West Africa Province, or ISWAP, which has become more prominent in carrying out abductions and attacks over the past year.

There are also fears that the ISWAP militants may now be operating in the country's northwest, too. Authorities confirmed recently that an extremist flag was seen flying in one town in northwest Niger state.