British stars including singer Sting and actresses Emma Thompson and Michelle Dockery have signed an open letter to the U.K.'s Prime Minister David Cameron urging him to provide a safe haven for the victims of civil war in Syria.

The note has been put together by officials at Amnesty International, Oxfam, and the Refugee Council, and it calls on the British leader to amend his pledge to help "several hundred" refugees.

It demands he find space in the U.K. to house "thousands" of displaced families from the war-torn region, and has been signed by stars including Vanessa Redgrave, moviemaker Ken Loach, Monty Python funnyman Michael Palin, and fashion designer Dame Vivienne Westwood.

The letter, addressed directly to the Prime Minister, states, "You promised to resettle some of the most vulnerable people fleeing conflict in the region... Given your promise and the U.K.'s proud tradition of offering protection to those who desperately need it, we couldn't have been more disappointed when we discovered the scale of your ambition for Syria's refugees; to resettle just 'several hundred people' over a three-year period...

"We can do better. We must do better. People's lives depend on it... The U.S. has pledge to offer thousands of places a year over many years. We are ashamed that the U.K. has failed to do likewise."

An estimated four million Syrians have been displaced by the country's civil war, which has raged since the Arab Spring uprising threatened to overthrow President Bashar al-Assad in 2011.