Kabul, Afghanistan (CNN) -- Several Afghan soldiers have been arrested after authorities found a number of suicide vests inside the country's Defense Ministry, a senior Afghan defense official said Tuesday.
The discovery triggered a lockdown of the ministry, which has since been lifted, said the official, who asked to remain anonymous because he is not authorized to speak to reporters.
The official could not confirm the number of arrests, and there was no comment on the report from the NATO command in Kabul.
Tuesday's discovery and arrests follow a series of attacks by Afghan security forces on American and allied troops in Afghanistan. So far this year, 16 of the 46 American service members killed in Afghanistan have died in what are called "green on blue" attacks, when Afghan troops turn their weapons on allied forces.
Two British service members and a U.S. soldier died in two separate attacks on Monday, while two senior U.S. officers were killed in the Afghan Interior Ministry headquarters in February.
Gen. John Allen, the commander of the NATO-led International Security Assistance Force, told a Washington audience Monday that the attacks have led to "an erosion of trust" among allied forces, "But I believe that the relationship is very strong nonetheless," he said.