* Worshippers leap from windows as shots ring out
* Boko Haram escalating campaign for Islamist state
* Military arrest suspect over car bomb blast (Adds ban on protests in Abuja over girls)
By Lanre Ola and Camillus Eboh
MAIDUGURI/ABUJA, June 2 (Reuters) - Gunmen opened fire on a church service in a remote village in northeastern Nigeria, killing nine people as worshippers fled into the bush, police and a witness said on Monday.
A member of the congregation said people jumped through windows to try to escape Sunday's attack in Attangara in the Gwoza hills - the main stronghold of Boko Haram militants waging an escalating campaign to carve out an Islamist state.
"As we were holding the service, we started hearing gunshots and everybody fled," Matha Yohana told Reuters.
"More than 10 of them (the gunmen) were riding motorcycles and one car," she said, adding some local people had pursued the attackers, killing four of them and capturing three. A police source said nine people were killed in the assault on the church.
Boko Haram has killed thousands since it started its campaign in 2009 and grabbed world headlines in April when it abducted more than 200 schoolgirls in another part of Borno state.
The mass kidnapping has piled political pressure on President Goodluck Jonathan, who on Thursday ordered a "full-scale operation" against the militants. He has accepted help from the United States and other foreign powers to try to free the girls.
Nigerians have protested almost every day since the girls were kidnapped, demanding action to free them. On Monday demonstrations were banned in the capital Abuja on the grounds they could be hijacked by "dangerous elements", a police statement said.
The assault on the church came the same day as a blast the army said was caused by a car bomb killed 18 people watching football on television in Kabang town in northeastern Adamawa state - another Boko Haram stronghold.
The military said on Monday they had arrested a man seen getting out of the vehicle that was carrying the explosive.
"A key suspect in the terror bomb explosion that rocked Kabang Community ... has been arrested by troops who cordoned (off the) area in swift response to the explosion," defence spokesman Brigadier General Chris Olukolade told Reuters by telephone from Abuja.
Boko Haram, seen as the main security threat to Africa's biggest economy and top oil producer, has set off several bombs across north and central Nigeria since April.
Adamawa, Borno and Yobe regions are under a state of emergency declared by the government in May last year.
The army said on Monday it had repelled an ambush and killed four militants in the Borno town of Biu and killed another five in a shootout in the state's Kawuri area, without saying when the clashes happened.
Boko Haram - whose name roughly translates as "Western education is sinful" - has attacked churches in the mainly Muslim north, as well as government targets and Islamic figures who do not back its tactics and severe interpretation of Islam.
The Organisation of Islamic Cooperation (OIC) on Monday released a statement branding the militants "outlaws".
"What they are doing is a criminal act, it has absolutely nothing to do with Islam," OIC secretary general Eyad Ameen Madani said when meeting President Jonathan in Abuja. (Additional reporting by Tim Cocks in Lagos, Anamesere Igboeroteonwu in Onitsha and Camillus Eboh in Abuja; Writing by Tim Cocks and Andrew Heavens; Editing by Andrew Roche)