By Adrian Croft

LONDON, March 12 (Reuters) - British Prime Minister Gordon Brown called on Wednesday for tougher measures against Sudan, including military sanctions, to halt the bloodshed in Darfur.

"This is a humanitarian tragedy of colossal proportions where the world must act," Brown told Britain's parliament.

"I believe we must strengthen our sanctions against the Sudanese government. We should have military sanctions for the whole of Sudan," he said.

Brown gave no details and did not specify whether he was talking about United Nations Security Council sanctions.

A government source said Britain would consider measures aimed at stemming the flow of weapons to both government and rebels in Sudan's western province of Darfur.

International experts estimate 200,000 people have died and 2.5 million have been forced to flee homes in Darfur since the conflict erupted in 2003, when rebels took up arms against the central government.

A 2005 U.N. arms embargo bans government transfers of weapons to Darfur. U.S. President George W. Bush said last May Washington would seek support for an expanded, international arms embargo on Sudan.

The U.N. has also imposed a travel ban and a freeze on overseas assets of four people.

Brown said he would like to move ahead with a no-fly zone for Darfur "if it were at all possible", and had discussed the idea with French President Nicolas Sarkozy, but stressed the difficulties of going ahead.

"We've got to accept that the area it would have to police is the geographical size of France. It would need large numbers of aeroplanes to be able to do so," he said.

"The more important thing at the moment is to get a ceasefire, to stop the aerial bombing of civilians," he said.

"I believe most of all that we must get people to the peace table," Brown said, adding that it was important the government as well as rebel groups join negotiations.

Of the five key Darfur rebel groups, only two have agreed to join talks, stalled since a failed summit in Libya in October.

Brown said Britain had asked China, an ally of the Sudanese government, to intervene over Darfur and said he would like U.N. Secretary General Ban Ki-moon to visit the region very soon.

The United Nations and African Union aim to have some 26,000 peacekeepers in Darfur, but only 9,000 are on the ground.

Western governments have accused Sudan's President Omar Hassan al-Bashir of delaying deployment by putting restrictions on the troops.

Brown said he had talked to Sarkozy about what they could do to provide helicopters that are urgently needed by the force, but announced no new steps. (Reporting by Adrian Croft; Editing by Catherine Evans)

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