Top military officials told lawmakers in a closed door briefing on Tuesday that they may not be able to shoot down every Iranian drone being launched against US military installations and assets in retaliatory attacks, according to two people familiar with the matter.

The officials, led by the chair of the joint chiefs of staff, Gen Dan Caine, said Iran has been deploying thousands of one-way attack drones and while they have capacity to take down the vast majority but not all of the barrage.

As a result, the officials said in a classified briefing for lawmakers on Capitol Hill, the US was focused on destroying the launch sites for the drones and conventional missiles as quickly as possible. The people spoke on the condition of anonymity to discuss sensitive details.

In retaliation against US strikes, Iran has been launching its low-cost, one-way attack Shahed drones. By flying low and slow, the drones are seen to be better able to evade conventional air defenses than ballistic missiles.