An alleged plot revealed last week to sabotage Sudan's security is linked to hardcore Islamist military officers and highlights turmoil within the regime of President Omar al-Bashir, analysts say.

Information Minister Ahmed Bilal Osman announced on Thursday the arrest of 13 people, including high-profile members of the security forces, who "targeted the stability of the state and some leaders of the state".

Unlike previous threats from political opponents, this one comes from within the military inner circles of Bashir's 23-year regime, said Khalid Tigani, an analyst and chief editor of the weekly economic newspaper Elaff.

"The government... has never been isolated like now," he said.

Tigani, a former activist in the National Islamic Front party which engineered the 1989 coup that brought Bashir to power, now calls himself an independent Muslim.

"This is a big mess," said Magdi El Gizouli, a fellow at the non-profit Rift Valley Institute of training and research, which focuses on Sudan and nearby countries.

He said that although the regime is battling insurgencies believed backed by neighbouring South Sudan in its border states, the major threat comes from closer to home.

"The biggest problem is in-house," Gizouli said.

Columnist Abdullah Rizig wrote in The Citizen newspaper on Sunday that the plot, about which officials have given only vague details, reflects "discontent and protest growing within the regime".

Information Minister Osman highlighted the arrest of Salah Gosh, who served as national intelligence chief until 2009.

But analysts focused on another name: armed forces Brigadier Mohammed Ibrahim, who played a role in the 1989 coup.

Earlier this year, he volunteered as a commander in the recapture of Sudan's Heglig oil field from occupying South Sudanese forces in what he considered to be a jihad or Islamic holy war, said Tigani.

"He's a hardcore Islamist with a long history of battle in South Sudan and so on," Gizouli added, referring to the 1983-2005 civil war that led to the South's separation last year.

He and Tigani named another arrested officer as Colonel Fateh Rahim Abdallah, who recently commanded the joint Sudan-Chad border force.

-- A return to Islamic values --

Most of the detained military men are close to a vocal group of ex-civil war volunteer mujahedeen fighters and an elite group within them called Al-Saeohoon or "tourists for the sake of God," Tigani said.

The war veterans, along with a youth movement within the ruling National Congress Party (NCP), have been calling for new national leadership and a return to Islamic values because they say the government is tainted by corruption and other problems.

Those seeking "reform" had hoped for change earlier this month at a congress of the Islamic Movement, a social group at the heart of the ruling NCP.

"I think their major concern... is to make the movement in charge of the government and its political party, and not the other way around," said Safwat Fanous, a political scientist at the University of Khartoum.

But the election of a regime loyalist to head the movement showed the reformers failed and the government had reinforced its control, he said.

The hard-core Islamists were so incensed that, fearing possible violence, the authorities took a pre-emptive move against them, Tigani said.

"Most people don't think there was a real move to topple the government," he said.

A witness saw armoured vehicles moving near Khartoum's airport about the time state-linked media revealed the "plot".

"They expected maybe a military showdown," Gizouli said.

But there was no gunfire -- only verbal volleys.

In a letter posted on some Internet sites and emailed to journalists on Saturday, London-based former mujahedeen Abdelghani Ahmed Edries warned the government "will pay a high price" if it harms those arrested.

"They are national heroes," he said, speaking for a group called the NCP Reform Forum.

What to do with those it has arrested is problem for the government in a country which has experienced at least seven coups or attempted coups in its 56-year history.

"They might try to talk to some, threaten others, and push some into exile," Gizouli said.

"I expect a great deal of suspicion on all sides."