The Afghan Defense Ministry went into a near-total lockdown Tuesday after the discovery of up to 11 suicide vests and the arrest of more than a dozen Afghan soldiers suspected of plotting to attack the ministry and blow up commuter buses for government employees, Afghan and Western officials told The New York Times.

The security breach took place in one of the most fortified parts of Kabul, less than a mile from the presidential palace and the headquarters of the American-led coalition, the Times reported.

Compounding the fears of renewed violence in Kabul was the apparent complicity of Afghan soldiers in the plot. Afghan soldiers and police officers have killed 15 of their colleagues among the international military force here at an alarming rate in recent months — about a quarter of all coalition soldiers killed, and second in number only to those killed in roadside bomb attacks.

The latest “green on blue” killings by Afghan security forces came Monday when two British soldiers and one American were killed in two separate attacks.

Gen. John Allen, commander of the International Security Assistance Force in Afghanistan, spoke to Pentagon reporters Monday about such attacks, and addressed “green on green” attacks as well — Afghans killing Afghans.

“The Afghans themselves,” Allen said, “who also suffer from what is euphemistically called green on green, they have taken a lot of steps themselves with an eight-step vetting process. They’ve worked very closely within the National Directorate of Security to place counterintelligence operatives inside their schools, inside their recruiting centers and inside their ranks, the idea being to spot and assess the potential emergence of an individual who could be an extremist or in fact a Taliban infiltrator. ...

“So I think between what the Afghans have done for themselves, what we’re doing for ourselves and how we’re partnering together, we seek to reduce this tragedy to the maximum extent possible.”

Details of the latest plot, which officials said was uncovered Monday, remained sketchy. The Defense Ministry denied any attempted bombings had taken place and said no soldiers had been arrested, calling a report by the BBC “quite imaginative and devoid of truth.”

But a Western official told the Times that at least 10 suicide vests were discovered in and around the ministry late on Monday afternoon. Most were found in guard sheds around a parking lot, the Times wrote.

An Afghan army officer at the ministry also said there were 10 bombers, and that they are believed to have been plotting to blow up buses. Some media reports said that there were 11 buses due to leave the ministry, which might have carried as many as 1,100 passengers, many of whom were to be Afghan soldiers.

The buses were due to set off just 45 minutes after the arrests were made, according to the BBC.

“You have to be cautious when you come here. It is not safe here,” said the officer, who also did not want to be identified. The plotters “have links inside the ministry. Otherwise, they could not enter such a highly secured place.”

Along with the usual contingent of Afghan Army guards, special army commandos could also be seen protecting the Defense Ministry on Tuesday afternoon, the Times reported.

A sergeant guarding the ministry told the Times that he and his men had been briefed on the plot, and that they were told the bombers may also have been planning to enter the ministry and possibly the headquarters of the intelligence agency.

The sergeant, who the Times wrote also asked not to be identified, said that two bombers might still be at large, thus the lockdown at the ministry, where only senior officers and people they escorted were being allowed in or out on Tuesday afternoon. He said that uniformed soldiers ordinarily walk into the ministry without being searched, an indication of a security weakness the plotters sought to exploit.

The Western official said a number of people, including Afghan soldiers, were arrested in connection with the plot Monday and Tuesday but could not provide an exact figure. Multiple Afghan television stations reported 10 arrests on Tuesday and six on Monday, although it was not clear whether the suspects were soldiers or civilians.

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