Footage of scores of girls kidnapped by Islamist militants in Nigeria demonstrates the "horror and barbarity" of the crime, Downing Street has said.
A video released by Boko Haram claims to show around 130 of the victims who were seized from a school last month.
The group's leader, Abubakar Shekau, is seen insisting that the girls will be held until all imprisoned militants have been freed.
There has been speculation that the comments could pave the way for a negotiated settlement, as Shekau has previously insisted the hostages would be sold.
Prime Minister David Cameron's spokesman said the Government had yet to examine the video in depth. "It underlines the horror and the barbarity of the actions in the kidnapping of these girls," the spokesman said.
"It underlines the importance of working with and in support of the Nigerian authorities and Nigerian people in terms of trying to bring about the release of the kidnapped girls, which is so important."
Earlier, Mr Cameron refused to criticise the response of the Nigerian authorities, telling LBC radio that everyone was working "around the clock" to try to free the victims.
"It's a very difficult situation," the premier added.