Mr Cameron stressed the importance of responding to the protests with reform not repression.
A Downing Street spokesperson said:
The Prime Minister spoke this evening with the King of Bahrain.
The Prime Minister stressed the importance of responding to peaceful protest through reform, not repression. The violence of previous days had been deeply concerning.
As a friend of Bahrain, the Prime Minister said that we supported the process of national dialogue which the Bahraini Government had initiated. All sides now needed to engage urgently with that process.
The Prime Minister is also following the situation in Libya closely. He is gravely concerned by reports of escalating violence and large numbers of civilian deaths. We condemn any use of force by the Libyan authorities against peaceful protesters. Such repression is unacceptable, counter-productive and wrong. The Libyan Government must listen to the views of its people and respond to them.