Hilary Benn has called for the UN to take over peacekeeping in Darfur, where he says security is deteriorating.
Two million people have been displaced by fighting in Darfur
The international development secretary said the efforts of African Union peacekeepers in the region were being hindered by the Sudanese government.
It comes a day after he pledged an extra £20m to support the peacekeepers. Peace talks are under way after fighting between the pro-government Janjaweed militias and rebels forced two million from their homes in Darfur.
Britain has already given £32m to supporting the 7,000-strong African Union force in addition to the £20m announced on Tuesday.
But Mr Benn, who is in the country meeting members of the Khartoum government, said the operation needed to be transferred to a larger and better-funded UN mission.
He told BBC Radio 4's Today programme: "The security situation has deteriorated compared with last June when I was last here in El-Fasher.
"The rebels have been responsible for an increasing proportion of the attacks. The Arab militia are still at work.
"It really reinforces the point that we have to step up the international effort here in Darfur."
He said international pressure also needed to be applied on those taking part in the long-running peace talks between the government and rebels in the Nigerian capital, Abuja.
The UN said in January that an expanded peacekeeping force was needed to cope with continuing violence in the region.
But the plan has been opposed by Sudan, which said funding should go to the African Union troops already there.
Mr Benn arrived in Darfur on Tuesday, where he visited refugee camps and members of the African Union mission.