The UN Security Council has approved sanctions against the Nigerian militant group Boko Haram, five weeks after it kidnapped more than 200 schoolgirls.

It will now be added to a list of al-Qaeda-linked organisations subject to an arms embargo and asset freeze.

US envoy Samantha Power said it was an "important step" in support of efforts to "defeat Boko Haram and hold its murderous leadership accountable".

It was earlier blamed for the deaths of 27 people in a north-eastern village.

Residents said gunmen had shot dead farm workers in Chikongudo, set fire to nearly all the homes there and stolen food in an attack on Wednesday night. The assailants stormed the village in cars and motorbikes, a trademark of Boko Haram, the residents added.

It came a day after twin bombings killed 122 in the central city of Jos. The authorities suspect Boko Haram of being behind them, but there has so far been no claim of responsibility from the group.

'Al-Qaeda training'

Boko Haram was added to the al-Qaeda Sanctions Committee's list of designated entities on Thursday at the request of Nigeria.

"Today, the Security Council took an important step in support of the government of Nigeria's efforts to defeat Boko Haram and hold its murderous leadership accountable for atrocities," Ms Power said.

The sanctions designation would help "close off important avenues of funding, travel and weapons" to the group, she added.

On Wednesday, Nigeria's permanent representative, U Joy Ogwu, said: "The important thing is to attack the problem, and that is terrorism."

The BBC's Barbara Plett Usher in New York says Boko Haram's links with al-Qaeda have come under scrutiny.

Reports quoting a draft UN document said its members had received training from al-Qaeda affiliates and fought alongside them in Mali.

Protests

Boko Haram, which has killed thousands of people in Nigeria through a wave of bombings and assassinations since 2009, is fighting to overthrow the government and create an Islamic state.

The government's failure to prevent attacks since launching an offensive against Boko Haram a year ago has triggered widespread anger.

On Thursday, protesters demanding the return of the schoolgirls snatched from their classrooms in the north-eastern town of Chibok and taken hostage five weeks ago were prevented from reaching the presidential villa in the capital, Abuja.

A statement from President Goodluck Jonathan read out to the demonstrators said the state was doing all it could to secure their release.

He also urged them to ensure their "zeal is matched with a realistic understanding of the situation".

The statement did little to placate the crowd, and one protester shouted: "Another small window for Jonathan and he refuses to use it."

Teachers across Nigeria also held a day of protests on Thursday in support of the abducted schoolgirls.

Teaching unions said they were also marching in memory of the 173 teachers killed by militants and called on the authorities to increase protection for schools, which were closed for the day.