Twenty-five renegade soldiers involved in an apparent coup plot in Guinea-Bissau are being detained in the capital and at an air base north of Bissau, an AFP reporter said, after the army uncovered a large cache of weapons.

The arms were seized at the homes of two soldiers arrested for taking part in Monday's attack on army headquarters which the regime has described as a coup bid.

Army chief General Antonio Indjai said he was "staggered" by the quantity of arms found during search operations in the northern suburb of Plack 1, at the homes of the soldiers who admitted taking part in the attack.

The army seized 30 Kalachnikovs, three rocket-launchers, a machine-gun, six crates of shells, three crates of flamethrowers, eight bulletproof jackets and ammunition in searches witnessed by AFP.

"I am surprised to see so many weapons which would have been used to destroy our country... I call on government to build secure armories to avoid having thousands of arms circulating outside of appropriate channels of control," Indjai told journalists.

On Monday, Indjai announced that a coup attempt by a group of renegade soldiers had been foiled.

The army said it had arrested controversial navy chief Rear Admiral Jose Americo Bubo Na Tchuto -- whom the United States has branded a drug kingpin -- as the "mastermind" of the plot.

Some observers put the mutiny down to a falling out between Indjai and Bubo Na Tchuto who was among 25 detainees paraded before journalists on Thursday.

Bubo Na Tchuto is being detained in Mansoa, 60 kilometres (40 miles) north of the capital, and the 24 others in four cells at a Bissau air base.

Another officer, General Watna Na Lai, was wounded and remains in hospital.

Bubo Na Tchuto told visiting journalists, human rights activists and NGOs he was "in good spirits".

But he criticised the conditions of his detention in a 20-square-metre (215-square-feet) office at the Mansoa garrison that had been turned into a cell.

"Since I was brought here, I haven't seen my doctor, I'm suffering from high blood pressure," he said, adding that he had not been able to see his family including his wife.

"When she sends food I never get it," he said.

In Bissau, journalists saw another 24 detainees held at the air base.

Journalists were not allowed to speak to them but members of NGOs who organised the visits said they also criticised the condition of their detention "in very small, badly lit cells with filthy toilets and without running water".

"We will plead with military authorities so the conditions of their detention are improved," Luis Vaz Martins, a member of an NGO that organised the visits, told the press.

He said none of the prisoners had been presented to a military investigating magistrate.

"Some have minor injuries, generally bruises suffered in their arrest; they did not suffer gunshot wounds but were beaten with clubs," Vaz Martins added.

Guinea-Bissau is notoriously unstable, with a history of coups and army mutinies, and has become a stomping ground for drug cartels which use it as a hub to traffic drugs to Europe.

The two soldiers targeted in Thursday's search were Sergeant Jose Batista Sambe from the navy and Antonio Mario Cabi, a former member of the presidential guard.

Sambe told journalists he led a commando unit in Monday's attack which was meant to "seize weapons to overthrow the current leadership of the army".

The two men said they were dissatisfied with poor salaries and living conditions in the impoverished former Portuguese colony.

Two people died on Tuesday in clashes between security forces and alleged mutineers as joint teams of soldiers, police and paramilitary police hunted suspects.