AFP - A Khartoum court condemned four Islamists to death on Wednesday for the 2008 killing of a US diplomat and his Sudanese driver, as the US embassy warned of possible retaliation over the verdict.

Judge Said Ahmed al-Badri sentenced the four to be hanged for the murders.

A fifth man, who had provided the other defendants with the weapon but did not take part in the murder, was sentenced to two years in prison.

John Granville, 33, who worked for the US Agency for International Development (USAID), and his 40-year-old Sudanese driver Abdel Rahman Abbas were shot dead in their car in Khartoum on January 1, 2008.

One of the four condemned men is the son of a leader of pacifist Islamist group Ansar al-Sunna, which is linked to Wahhabism -- a hardline form of Sunni Islam practised mainly in Saudi Arabia-- but is not involved in politics.

A group calling itself Ansar al-Tawhid had claimed the New Year's Day murder according to SITE, a US-based organisation which monitors Islamist websites.

It said the murder was in response to attempts to raise the banner of Christianity over Sudan, the largest country in Africa.

The US embassy in Khartoum had urged personnel and citizens to keep a low profile if the court found the defendants guilty.

"Should the court announce guilty verdicts in this case on June 24, the reaction among the men's supporters could include demonstrations at Embassy Khartoum facilities and/or other anti-American, anti-Western actions," the embassy warned in a statement.

"US citizens are advised to avoid the Khartoum North courthouse, located in downtown Khartoum, maintain a low profile, and increase vigilance," it said.

Relations between Sudan and the United States have long been strained, most recently over the six-year conflict in the western region of Darfur over which Washington has accused Khartoum of genocide.