KHARTOUM (AFP) - At least 29 people have been killed in three days of rioting in Sudan sparked by a government decision to scrap subsidies on fuel, medical officials said on Thursday.

"We have received the bodies of 21 people" since the protests began on Monday, a hospital source in Khartoum's twin city Omdurman told AFP, adding that all were "civilians".

Another eight people were killed in other regions, witnesses and families said.

Activists have called for fresh protests on Thursday in Khartoum, where anti-riot forces have been deployed since early morning at major road intersections, an AFP correspondent said.

The protests have been the largest in Sudan since President Omar al-Bashir seized power in 1989.

The US embassy called on its citizens to avoid flashpoint areas, saying it had received "regrettable" reports of casualties and warning Americans of the danger of further protests.

Riots broke out in several districts of the capital on Wednesday, some near the city centre, and public transport ground to a halt, an AFP correspondent reported.

The protests first erupted in Wad Madani in Gezira state south of Khartoum, the scene of the first death on Monday. They have also spread to Nyala, the capital of South Darfur state.

The education authorities have announced the closure of schools until September 30.

The Internet remained cut on Thursday, users said, but it was still not known if the reason was a technical failure or a deliberate move by authorities.