Sudan arrested its former spy chief and other senior military and security officers yesterday after foiling what officials said was a plot to incite chaos and target leaders.
Witnesses said they saw army tanks and armoured vehicles moving down a main street in the centre of Khartoum around midnight, but life in the city was normal during the day with shops in the centre bustling.
Sudan's President Lieutenant General Omar al-Bashir has kept up a 23-year hold on power, even as a series of uprisings troubled the country's poor border areas, including the region of Darfur.
Salah Gosh, former head of Sudan's powerful intelligence and security agency, was arrested with others on suspicion of "inciting chaos", "targeting" some leaders and spreading rumours about Bashir's health, Information Minister Ahmed Belal Osman said.
Bashir, 68, has undergone throat surgery twice since the summer. Officials insist he is in good health.
"The situation is now totally stable," Osman said, naming Gosh and two other arrested officers including Wad Ibrahim, a prominent Islamist in the army.
Some Islamists inside the army and the ruling National Congress Party have said that Bashir and other senior leaders had abandoned the religious values of the 1989 coup and had concentrated decision-making in the hands of too few people.
Some also feel Bashir has been too soft on South Sudan, which temporarily wrong-footed the Sudanese army by seizing a major oilfield during border fighting in April - a shock to many officers.
Gosh was once among Sudan's most influential officials. As chief of the National Intelligence and Security Service, he headed what is one of the country's most powerful institutions, alongside the army. But Bashir removed him as spy chief in 2009.
A leaked US diplomatic cable from 2008 quoted a government official as saying Gosh had mused about the possibility that an International Criminal Court arrest warrant for Bashir could lead some to try to replace him.
"Conspiracy and plotting is like breathing in Sudan," the cable noted.