The Prime Minister pledged his "unstinting" support for attempts to seek reconciliation between the east African country's political leaders, whom he has urged to exercise restraint.

Mr Brown has asked Kenyan President Mwai Kibaki and opposition leader Raila Odinga to help stop the violence and appealed for international support.

He spoke to Ghanaian president John Kufuor, chairman of the African Union, and Ahmed Tejan Kabbah, head of the Commonwealth observer mission in Kenya, about overseeing a process of reconciliation.

In a statement, he said: "I am gravely concerned by the situation in Kenya."

As violence escalated in Kenya, Mr Brown went on: "I have urged both Mwai Kibaki and Raila Odinga to exercise restraint and responsible leadership.

"Following my discussions with them, with President Kufuor of Ghana, and with former president Kabbah of Sierra Leone, I welcome President Kuffuor's decision to help with a process of dialogue and reconciliation.

"This offers an opportunity to stop the violence and to help Kenyans unite. Presidents Kufuor and Kabbah have my unstinting support in this essential task."

Thousands of British tourists in Kenya have been advised to stay indoors with post-election violence continuing.

The Foreign Office advised against all but essential travel to areas of the East African country's two biggest towns.