The Islamist group Boko Haram has seized Chibok, the Nigerian town from which it kidnapped 276 schoolgirls earlier this year, in a show of strength that makes the teenagers’ safe release a more distant prospect than ever.

The militants attacked at about 4pm on Thursday, destroying communications masts and forcing residents to flee, according to witnesses. One described running past bodies strewn on a street.

The fall of Chibok is hugely symbolic. The town in north-east Nigeria became the centre of world attention in April when Boko Haram fighters stormed the government girls secondary school, forced students onto trucks and drove them into the bush. There was a global Twitter campaign, BringBackOurGirls, and criticism of the government’s response.

Tsambido Hosea Abana, a community leader from Chibok who has cousins and nieces among the 219 teenagers still being held, said on Friday: “Our girls are in the bush and they are killing the parents. We are talking about the lives of the parents and adults now. This thing has gone beyond anyone’s control.”

Speaking from the capital, Abuja, Abanda said he had sisters, aunts, uncles, nieces and nephews in Chibok. “I’ve only heard from one. He was on his way to Chibok and he met people running away so he turned around. A villager told me he saw corpses lying in the street; he could not count them because he was running.”

He joined criticism of the military’s handling of the crisis. “They are not doing well. How can they just run away when they hear ‘Allahu Akbar’? They are handing over weapons to these boys.”

Boko Haram’s leader, Abubakar Shekau, claims to have carried through his promise to marry off the teenagers still being held and said they had all converted to Islam.

Enoch Mark, a Christian pastor whose daughter and niece are among the kidnapped, told Agence France-Presse “Chibok was taken by Boko Haram. They are in control.”

Mark said the attack on the town, which residents have warned of for some time, appeared to come after Boko Haram overran the towns of Hong and Gombi in neighbouring Adamawa state. “They came in and engaged soldiers and vigilantes in a gunfight,” he added.

“Some of us managed to escape. All the telecom towers in the town were destroyed during the attack with RPGs [rocket-propelled grenades]. No one can say what the situation is in the town in terms of destruction to property.”

Pogo Bitrus, chairman of the elders forum in Chibok, also confirmed the attack but said Boko Haram may have had inside information about security. “The vigilantes use shotguns and cartridges and have been short in supply, so the leader left yesterday for Maiduguri to procure more in the event of any attack,” he told AFP.

“But Boko Haram launched the attack while he was still in Maiduguri. He was due to come today, so it looks like they knew what was happening.”

Bitrus said the vigilantes were preparing for a counter-attack and troops had been deployed from Damboa, 22 miles away by road to the north-west. “I can assure you they are going to retake Chibok,” he added.

Boko Haram – whose name means “western education is sinful” – have been waging a deadly five-year insurgency aimed at creating a hardline Islamist state in the north of Africa’s most populous country. In October the government announced a ceasefire had been agreed, but the group’s leader denied this and has intensified attacks since.

Last Monday, 58 boys were killed when a suspected Boko Haram suicide attacker detonated explosives at a school in Potiskum, Yobe state.

Two weeks ago it took the commercial hub of Mubi, killing dozens and torching houses, and renamed it “Madinatul Islam” (“City of Islam” in Arabic), residents told AFP. It introduced its strict version of Islamic law, including amputations for alleged thieves.

However, in a rare setback, about 200 vigilantes and hunters armed with bows and arrows, clubs, spears, machetes and home-made guns helped the Nigerian military regain control of Mubi, which had been the biggest town under the extremists’ control.

One resident, who asked not to be named, told AFP: “I saw the Boko Haram fighters fleeing in droves in their vehicles when the hunters and vigilantes entered the town.

“Their emir [leader] was captured by the hunters and made to sit outside the military barracks that he and his men turned into their base. He had his hands tied from the back and we swarmed to have a look but we were later dispersed by the hunters.”

Mubi is the first town Boko Haram has lost since August, when it declared a caliphate in areas under its control. But celebrations were cut short when Boko Haram fighters seized the towns of Gombi, Hong and the major prize of Chibok.

Earlier this week president Goodluck Jonathan, whose leadership during the crisis has been widely questioned, announced his intention to seek another term in office, pledging to defeat the insurgents and free the schoolgirls.