* Gunmen attack three villages in Gwoza area of Borno state
* Girls' who escaped Boko Haram get psychiatric help
* Archbishop of Canterbury condoles Nigeria on visit (Adds psychiatric help for parents, Archbishop of Canterbury)
By Lanre Ola
MAIDUGURI, Nigeria, June 4 (Reuters) - Suspected Islamist militants have killed dozens of civilians in three villages in northeastern Nigeria, a region now hit by almost daily attacks, a security source and a victim's relative said on Wednesday.
Gunmen in combat uniforms rode army trucks on Tuesday through Borno state's Gwoza area, the main stronghold of the Boko Haram militant group, firing on villagers and burning houses and churches to the ground, the security source said.
Andrew Tada, a Gwoza man living living in Borno's capital Maiduguri, said he lost two cousins in the attack. He said residents had told him they were preparing to bury 45 people from one village alone.
"It is very sad and the villages are deserted now," he said. "We are just asking government to give us security to go there tomorrow to evacuate the corpses for burial."
Boko Haram has killed thousands since 2009 and grabbed world headlines after it abducted more than 200 girls from a secondary school in Borno's town of Chibok in April.
The orgy of killing has continued with more than 560 civilians killed by insurgents since April 14, the day of the abduction and a deadly bus park bomb in Nigeria's capital Abuja.
In one of the deadliest incidents, a bomb in the central city of Jos last month killed 118 people, officials said.
The mass kidnapping and bombings have piled political pressure on President Goodluck Jonathan, who on Thursday ordered a "full-scale operation" against Boko Haram.
The Archbishop of Canterbury Justin Welby, who used to live in Nigeria, paid a visit to Goodluck Jonathan on Wednesday, to express condolences for the near daily atrocities carried out by the insurgents fighting for an Islamic state.
He expressed "sympathy for the struggles and suffering of the recent days" and said he was "deeply saddened by the bombings in Jos," because he knew the city well.
The security source said about three-quarters of the residents in the three villages near the Cameroon border - Attagara, Agapalawa and Aganjara - were Christians, but he did not know if Tuesday's attacks had targeted them specifically.
Boko Haram often targets Christians and has bombed several churches, although most of its victims have been Muslim.
United States troops are in neighboring Chad on a mission to find the abducted girls. Britain and France have also offered help, but Nigerian authorities fear any rescue mission could endanger their lives.
Of the 276 girls the militants kidnapped, 57 escaped in the early days of the abduction, according to officials in the Borno state government.
A USAID-backed inter-faith group arrived in Maiduguri on Wednesday to offer psychiatric help to the girls' parents.
"This is our contribution: to help the girls' recover from trauma of the attack on their school by Boko Haram," James Wuye, co director of Nigeria-based Inter-Faith Mediation Center, said. (Additional reporting by Abraham Terngu in Abuja; Writing by Tim Cocks; Editing by Tom Heneghan)