KABUL, Afghanistan — Two European allies of the United States have been directly participating in so-called kill decisions against insurgents in Afghanistan despite rules prohibiting them from doing so, according to two senior Western officials with knowledge of the operations.

The accusations concern airstrikes, mostly by drones, that American officials have justified as part of a lasting counterterrorism mission agreed to with the Afghan government. However, some of the strikes have come under question as being far more aggressive than the security deal allows for.

The two countries said to be improperly involved in approving strike decisions — Germany, a NATO member of the coalition in Afghanistan, and Sweden, which is not a member of NATO — as well as a spokesman for the American-led military coalition all denied that anyone other than the United States military had been involved in targeting insurgents.

But the two senior officials said that the issue, which has not been publicly disclosed previously, has been quietly increasing tensions between the American military and its NATO and other allies. And the accusations are likely to cause a particular stir in Germany, where constitutional rules forbid offensive military operations in most cases and where human rights groups have joined lawsuits that alleged even indirect German assistance for American drone strikes.