LONDON, Sept 16 (Reuters) - Britain's Prime Minister Gordon Brown on Sunday pledged technical support for peacekeepers due to go to Sudan's Darfur region, but warned Khartoum of possible further sanctions if it failed to make "necessary changes".

He was speaking in a BBC interview as human rights groups prepared protests and marches in a "Global Day for Darfur" in around 30 countries including Britain.

Brown described as "one of the great tragedies of our time" the 4 1/2-year Darfur conflict, in which international experts say some 200,000 people have died and 2.5 million have been driven from their homes. Khartoum disputes the figures.

The Sudanese government and Darfur rebels are to hold peace talks on Oct. 27 in Libya under the auspices of the United Nations and African Union.

Britain, Sudan's former colonial ruler, says it will not contribute soldiers to the 26,000-strong joint U.N. and African Union peacekeepers in line with Khartoum's demand for a predominantly African presence in Darfur.

Brown's promise of "technical help" was understood to mean airlifting African peacekeepers to the region or possibly supplying equipment to help them operate.

Brown told the BBC a ceasefire and political settlement was needed.

"If that were to happen, we'd be prepared to give economic assistance so that the people of Darfur were in a better position and we can start to rebuild.

"If it doesn't work and we find that the government of Sudan is not making the changes necessary, then we will have to move to further sanctions," he said in remarks on the BBC Web site.

Sudan signed a joint statement with the United Nations this month agreeing to end violence in Darfur, prepare for the peace talks and help deploy the peacekeepers.

Brown said the peacekeeping force should be deployed this year, but officials have indicated next year was more likely.

British Foreign Office Minister for Africa Mark Malloch Brown said in an interview with the Observer on Sunday that the peacekeepers expected a fight with groups like the government-allied Arab militias known as the Janjaweed.

"I'm sure the forces will be tested early on by "janjaweed" elements who want to humiliate it. But this is an enforcement force not an observation force. It will be stepping in to protect civilians who are under attack," said Malloch Brown, who visited Darfur this month.

Britain and France last month revived the spectre of sanctions against Khartoum if progress is not made on a Darfur ceasefire and at the peace talks. The United States has also threatened wider sanctions.

The U.N. Security Council has already imposed an arms embargo on rebels and militia but not on the government.

China is to send more than 300 engineering troops to Darfur next month to help prepare for the peacekeeping force, but Beijing has been seen as the main opponent on the U.N. Security Council to Western moves for sanctions.

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