The Afghan general in charge of security at the ministry of defence in Kabul on Wednesday flatly denied reports by local and foreign media that a huge suicide attack had been foiled at the compound.

General Omar Zadran, commander of the ministry of defence support and security brigade, blamed foreign spy services -- among them Pakistan and Iran -- trying to destabilise Afghanistan for the confusion.

Reports on the BBC, citing Afghan intelligence sources, said that first 11, then a total of 18 people, many of them Afghan soldiers, had been arrested at the ministry compound, and suicide vests and explosives recovered near the car park.

It was suggested that as many as 1,100 employees could have been targeted.

The BBC report was followed up by private Afghan television station TV1 and The New York Times, which quoted anonymous Afghan and Western sources and said a lockdown had been imposed at the ministry.

One Afghan intelligence source told AFP that 11 people had been arrested, including an unspecified number of soldiers, and suicide vests and explosives found, although further details were limited.

But Aimal Faizi, spokesman for Afghan President Hamid Karzai, said: "There is no truth in this at all. It's absolutely not true."

Zadran told AFP he had called a drill with a scenario of an attempt to poison the ministry's thousands of employees, and suicide attackers targeting the compound kitchens.

"We issued an alarm to check how quick our units reacted. That's probably the reason the journalists got it wrong," he said.

He accused regional intelligence services' agents of planting the initial reports that a suicide attack had been prevented.

"This is mainly an intelligence war, and this war is escalating," he said. "These guys are here, there and everywhere trying to do everything to destroy the image of prominent people inside the government."

Brigadier-General Dawlat Waziri, one of the ministry's spokesmen, also blamed foreign agencies, adding: "I can assure you there was no incident of any kind.

He insisted that the defence ministry's relationship with Afghan intelligence and other security services was good.

"I don't believe such propaganda or lies could spread to media outlets from Afghan security entities," he said, but added: "It could be the work of an individual making such claims."

Officials of the Kabul government often blame Afghanistan's neighbours for the country's woes.

A Western security source in Kabul -- who said he had no knowledge of the reported plot -- suggested the rumours could be the result of different arms of the Afghan security services manoeuvring against each other.

A suicide attack involving 11 assailants would have been one of the biggest in the decade-long conflict in Afghanistan, where US-led NATO troops and Afghan security forces are battling to reverse a Taliban insurgency.

The speed with which the claims circulated illustrates the febrile atmosphere in the Afghan capital in the wake of a series of killings by members of the Afghan security forces.

The reports first surfaced a day after two British and one American soldier were shot dead by Afghan security personnel in two separate incidents.

Such attacks, known as "green on blue", have killed 17 NATO soldiers so far this year, more than one in six of their fatalities in 2012.

The deaths have ramped up tensions and threaten to undermine the West's plan to train Afghans to take over security by the end of 2014, allowing NATO combat troops to withdraw after a long and costly war against the Taliban.

The US military has said that most of the attacks are not the result of Taliban infiltration. Assailants are "generally self-radicalised", according to General John Allen, the US commander in Afghanistan.