Four Sudanese men have been condemned to death by a Khartoum court for killing a US diplomat and his Sudanese driver.

Said Ahmed al-Badri, the judge, sentenced the four to be hanged for the murders on Wednesday.

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

John Granville, 33, a former official at the US Agency for International Development, and Abdel Rahman Abbas, his 40-year-old Sudanese driver, were shot dead in their car in the capital on January 1, 2008.

Granville was the first US government official killed in Khartoum in more than three decades.

One of the four condemned men is the son of a leader of Ansar al-Sunna, an Islamist group, which is linked to Wahhabism - a form of Sunni Islam practised mainly in Saudi Arabia.

A group calling itself Ansar al-Tawhid had claimed responsibility for the murders, SITE, an organisation which monitors Islamist websites, said.

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

Ahead of the verdict, 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 said 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.