More than 200 combatants have been killed after Nigerian troops clashed with Islamic extremists who attacked the north-eastern city of Maiduguri on Sunday.

As the battle raged, suspected Boko Haram insurgents continued scorched-earth attacks on villages some 200km (125 miles) to the south in Adamawa state.

Survivors reported that the rebels rampaged through villages slitting throats of residents, looting and burning homes and abducting dozens of trapped women and children.

Adamawa state legislator Adamu Kamale appealed for troops to protect civilians in Michika, where six villages were under attack. “The attacks have continued since Friday with no presence of security operatives,” he said.

The attacks come as US secretary of state John Kerry visited Lagos, Nigeria’s commercial capital, to encourage peaceful elections on 14 February.

“This will be the largest democratic election on the continent,” Kerry said. “Given the stakes, it’s absolutely critical that these elections be conducted peacefully — that they are credible, transparent and accountable.”

In Maiduguri, troops blocked roads into the city, which also prevented civilians from escaping.

Defense ministry spokesman General Chris Olukolade said on Sunday evening that troops successfully repelled attacks on Maiduguri and Konduga, 40km to the southeast.

But he said the military was mounting air raids in Monduno, a town 140km northeast of Maiduguri, which Boko Haram seized Sunday morning.

More than 200 combatants died on Sunday, mainly insurgents, according to soldiers and civilian fighters who counted bodies.

In Lagos, Kerry met the Nigerian president Goodluck Jonathan and his chief rival candidate, former military dictator Muhammadu Buhari. Kerry told reporters afterward that he won pledges from both to refrain from violence.

He also issued a warning that anyone responsible for inciting post-election mayhem would be barred entry to the United States, where millions of Nigerians live.

Kerry promised more US support in the fight against Boko Haram if the elections take place peacefully and democratically.

More than 800 people were killed in protests in the north of the country after Buhari, a Muslim northerner, lost 2011 elections to Jonathan, a Christian from the south.

Boko Haram has denounced democracy and wants to make Nigeria an Islamic state. The population of about 170m is divided almost equally between Muslims in the north and Christians in the south.

Jonathan made a surprise visit to Maiduguri 10 days ago and pledged to crush the insurgents. But his repeated promises are ringing hollow as Boko Haram since August has seized and kept control of large swaths of the northeast, including key border crossings into Cameroon, Chad and Niger.

With encouragement from the United Nations, Nigeria and its neighbors are setting up a multinational force to fight the extremists who recently have increased cross-border raids into Cameroon.

But there is distrust of Nigeria’s military, which many believe is infiltrated by Boko Haram at the highest levels.

The Maiduguri attack was not unexpected. Earlier this month, Boko Haram on seized a military base and Baga town on the border with Cameroon, killing hundreds of civilians and leaving the main road open to Maiduguri.

Maiduguri is the birthplace of Boko Haram and has been attacked many times in the five-year Islamic insurgency that killed 10,000 people last year.