Sudan's information ministry says the country's interim Prime Minister Abdulla Hamdok is under house arrest and being forced to issue a message in support of a military coup.
The news comes as the United States expressed alarm over recent developments in the country, in a transition to democracy for more than two years after former autocrat Omar al-Bashir was removed from power. US Special Envoy to the Horn of Africa Jeffrey Feltman said Washington was "deeply alarmed" by reports of the military takeover.
The ministry said the internet had been cut off and military forces closed bridges. The country's state news channel played patriotic traditional music and scenes of the Nile river. The Umma Party, the country's largest political party, described the arrests as an attempted coup, and called on people to take to the streets in resistance. Earlier, the Sudanese Professionals' Association, a group leading demands for a transition to democracy, issued a similar call.
A possible takeover by the military would be a major setback for Sudan, which has grappled with a transition to democracy since long-time autocrat Omar al-Bashir was toppled by mass protests.
Monday's arrests come after weeks of rising tensions between Sudan's civilian and military leaders. A failed coup attempt in September fractured the country along old lines, pitting more-conservative Islamists who want a military government against those who toppled al-Bashir more than two years ago in mass protests. In recent days, both camps have taken to the street in demonstrations.