* Gunmen set off bombs, fire on congregation
* Islamist Boko Haram often target Christians
* Nigerian forces are struggling to contain insurgency (Adds details, background)
By Imma Ande
YOLA, Nigeria, Jan 27 (Reuters) - Attackers armed with guns and explosives killed 22 people at a busy church service in a northeast Nigerian village, witnesses said on Monday, in a region where Islamist sect Boko Haram is resisting a military crackdown.
They set off bombs and fired into the congregation in the Catholic church in Waga Chakawa village in Adamawa state on Sunday morning, before burning houses and taking residents hostage during a four-hour siege, witnesses said.
President Goodluck Jonathan is struggling to contain Boko Haram in remote rural regions in the country's northeast corner, where the sect first launched an uprising in 2009.
The shady sect, which wants to impose sharia law on a country split roughly equally between Christians and Muslims, has killed thousands over the past four and a half years and is considered the biggest security risk in Africa's top oil exporter and second largest economy after South Africa.
Its fighters' favourite targets have traditionally been security forces, politicians who oppose them and Christian minorities in the largely Muslim north.
The spokesman for the Catholic Diocese of Yola, Reverend Father Raymond Danbouye, confirmed 22 people killed in the attack were buried at a funeral on Monday.
The military and police did not respond to requests for comment but one army source confirmed the attack, asking not to be named because he wasn't authorised to speak with the media.
Waga Chakawa is near the border with Borno state, in which there was a separate assault on Monday by suspected members of the shady sect in Kawuri village, witnesses said.
Residents of that village who fled to the state capital Maiduguri said gunmen killed several people and set homes ablaze in the early morning attack.
An army spokesman did not respond to requests for comment.
Jonathan replaced his chiefs of defence, army, navy and air force last week in a widespread military shake-up. No reason was given for the overhaul, but security experts believe there was a need for a change of tactics in combating Boko Haram.
Jonathan declared a state of emergency in three northeastern states in May last year and launched an intensified military campaign to try to end the insurgency. (Reporting by Imma Ande; Writing by Joe Brock; Editing by Tim Cocks and Alister Doyle)