The United States condemned a crackdown on anti-government protests in Sudan that have spread throughout the capital, Khartoum.

The unrest that began as isolated student protests over planned austerity measures in the Arab-African nation expanded over the past several days into larger and more volatile demonstrations.

Riot police were ordered in to immediately stop the street uprising, firing tear gas and using batons on rock-throwing demonstrators, Reuters reports.

There have also been reports that protesters have been arrested, detained and beaten, the U.S. State Department said in a statement.

"The heavy-handed approach adopted by Sudanese security forces is disproportionate and deeply concerning," said State Department spokeswoman Victoria Nuland.

Sudanese authorities have downplayed the protests as the work of agitators.

Activists have sought to use public frustration to build a movement to topple the government of President Omar Hassan al-Bashir.

Soaring inflation has gripped the country since South Sudan seceded a year ago - taking with it about three quarters of the country's oil production.