Sudan has expelled a foreign journalist for reporting on the country's Darfur crisis and arms industry, U.S. diplomats said on Monday.

Canadian-Egyptian reporter Heba Aly, who wrote for U.S. news agency Bloomberg, the Boston-based Christian Science Monitor newspaper and the United Nations news service IRIN, left the country last week.

She told colleagues that officers from Sudan's security service contacted her and ordered her to leave days after she made enquiries about a Khartoum-based arms manufacturer.

"The U.S. embassy in Khartoum condemns this expulsion and continues to deplore infringements by the Government of Sudan upon freedom of the press and expression," the embassy said in a statement.

No one was immediately available for comment from Sudan's government or security service.

Aly reported on a series of clashes between government forces and rebel fighters in Sudan's Darfur region. Foreign journalists receive permits to visit the remote western region, but have faced restrictions on their movements once they arrive.

Freedom of the press is guaranteed in Sudan's constitution. But local journalists regularly complain about censorship, the detention of reporters and the seizure of newspaper print-runs.

Media rights groups Reporters Without Borders said it was investigating Aly's case.