* Suspected Islamist militants rounded up, shot villagers
* Incident near state capital a day after scores killed in 3 villages
* President under pressure over insurgency, mass abduction (Recasts)
By Lanre Ola
MAIDUGURI, Nigeria, June 5 (Reuters) - Suspected Islamist militants pretending to be preachers rounded up and killed at least 42 villagers in northeastern Nigeria, a police source said, as an escalating insurgency increasingly targets civilians.
The shootings on the outskirts of the city of Maiduguri late on Wednesday came a day after officials said raiders killed scores in three other settlements in Borno state, where the Boko Haram militant group first launched its campaign to carve out an Islamist caliphate.
The attackers, who were wearing military-style uniforms, drove into the village of Bardari, told people to gather for a sermon and opened fire, the police source told Reuters. "The people couldn't identify them in time as terrorists," the source added.
No group claimed responsibility for the attack. But Boko Haram has stepped up its revolt and mounted nearly daily attacks in the area since it made world headlines in April by abducting more than 200 schoolgirls in another part of the state.
The mass abduction, and Boko Haram's fightback against a military offensive, has increased political pressure President Goodluck Jonathan, who has faced regular street protests by activists criticising his response.
Jonathan has accepted help from the United States and other foreign powers who are alarmed at the prospect of further turmoil in Africa's largest economy and oil producer, and its potential impact on a fragile region. Borno state borders Niger, Chad and Cameroon.
After Wednesday's shooting, militants then left, crossing a river and setting fire to houses in the neighbouring village of Kayamla, said the police source.
"Boko Haram wreaked havoc in the villages. They burned houses and killed people mercilessly after tricking the residents," said Saleh Mohammed, a member of Civilian JTF - one of a number of vigilante groups that have sprung up to try to fight back.
Mohammed, who visited the site on Thursday, said survivors had told him the attackers pretended to be itinerant preachers.
Civilian vigilante groups, and villages seen as supporting then, have faced revenge attacks blamed on Boko Haram, which had focused mostly on military and government targets in the early days of its revolt.
Boko Haram has no direct line of communication with the Western press and its purported leader, Abubakar Shekau, only occasionally claims attacks through videos circulated to local journalists.
Jonathan and the army have said they are doing all they can to release the girls, but have warned any attempt to free them by force could put them at risk, while any deals or prisoner swaps could encourage more kidnappings.
Britain's Foreign Secretary William Hague will host a meeting of African and Western officials in London next week aimed at stepping up efforts to defeat Boko Haram, his office said on Thursday. (Writing by Andrew Heavens; Editing by John Stonestreet)