Eight more girls have reportedly been kidnapped by militant group Boko Haram in north-eastern Nigeria.

The girls, aged 12 to 15, were abducted near one of the Islamist militant group's strongholds.

Lazarus Musa, a resident of Warabe, where the attack happened, said: "They were many, and all of them carried guns. They came in two vehicles painted in army colour.

"They started shooting in our village."

A police source, who could not be named, said the girls were taken away on trucks, along with stolen livestock and food.

Boko Haram is already threatening to sell more than 200 schoolgirls it abducted last month.

Earlier, the UK offered help to Nigeria to try to secure their release.

British Foreign Secretary William Hague revealed the country's potential involvement in the case after the militant group threatened to sell the abducted girls.

"We are offering practical help," he told reporters as he arrived for a Council of Europe meeting in Vienna to discuss ways to defuse the crisis in Ukraine

He said he did not want to discuss exactly what help Britain was offering, just as US authorities have avoided going into detail.

It is thought Nigeria has so far not accepted either country's offer.