LONDON – Britain’s foreign secretary, Jack Straw, flies to Sudan today to press the Khartoum government to rein in militias waging a campaign of terrorism in the western province of Darfur.

Britain says that “no option has been ruled out,” including military intervention, to halt the world’s worst refugee crisis. More than 50,000 people have died in the conflict.

But senior officials say they are focusing on promoting “an African solution.” After the wars in Afghanistan and Iraq, Britain is reluctant to become involved in more military action that could be presented as a Western attack on an Arab or Muslim country. Instead, it is supporting the peace talks between Khartoum and Darfur rebels that will be chaired by Nigeria today. It is also providing support behind the scenes, including money and expertise, for an African monitoring force that is starting to deploy in Darfur.

British officials say they will back a tenfold expansion of the African Union force of 300 and are urging Arab countries to contribute troops.

Mr. Straw will tell the Sudanese government to do more to end the “impunity” of the Janjaweed, a militia of nomads accused of killing thousands of villagers and driving more than a million out of their homes.

Critics argue that it is naive to expect the government, which is accused of supporting the Janjaweed, to restore security. But a senior British official said: “The most effective way to provide security in Darfur is to encourage the Sudanese government to do so. Having an external monitoring force is important to that aim.”

The United Nations Security Council has given Khartoum until next Monday to disarm the Janjaweed or face unspecified “measures.” In Britain’s view, Sudan’s response has been mixed. The flow of humanitarian aid has improved and the government has sent more police to Darfur.

Britain is willing to give Khartoum the benefit of the doubt, saying that it is difficult to establish precisely what is happening in a remote region the size of France.

An official said: “Nobody has ever been completely in control of Darfur, including the British.” He added: “The natural instinct of the Security Council will not be to slap heavy-duty sanctions on Sudan.”

There has been long-running rivalry between nomads and villagers in Darfur, but the conflict intensified 18 months ago when two rebel groups rose up against Khartoum. Human rights groups say the Janjaweed are being supported by the government, which has even used aircraft to bomb African villagers.

The first contingent of 150 Rwandan troops has arrived in Darfur, to be followed by a similar number of Nigerian troops.