Eighteen Yemeni civilians have been killed this week in two separate attacks by U.S. military drones.

Security officials in Yemen said 15 people traveling in a convoy were killed in an air strike on Thursday, Reuters reported. The convoy was suspected of belonging to al Qaeda. The group was on their way to a wedding, Reuters reported.

Local sources where the strike hit in the al-Bayda province say it was a drone, Reuters reported.

"An air strike missed its target and hit a wedding car convoy, ten people were killed immediately and another five who were injured died after being admitted to the hospital," one official told Reuters. Five more people were also injured.

A similar attack occurred on Monday that killed three people also traveling by car. Missiles fired from the drone attacked a car that was driving on a road in al-Qatan, part of the Hadramout province, Reuters reported.

"The vehicle and its occupants were completely burned," a Yemeni official told Reuters. The official did not say who the victims were.

The U.S. has recently increased air strikes using drones, aircrafts that are unmanned, in the fight against Islamist militant group al Qaeda. The U.S. considers the Arabian Peninsula a stronghold for the group. Though Washington confirms using drones in Yemen, it does not openly comment on the matter, Reuters reported.

Despite the casualties the drone strikes persist. A Human Rights Watch report from August said that U.S. military strikes in general have killed many Yemeni civilians. The report specified there were six "unacknowledged" attacks in Yemen that had nearly or actually violated international law, Reuters reported.

Maintaining order in Yemen is not only a concern of the U.S. If instability in Yemen persists, the fear is that conflict could spread to neighboring Saudi Arabia, a major oil producer, Reuters reported.