A U.S. drone strike in Somalia "most likely" killed Hassan Ali Dhoore, a senior leader of the terror group al-Shabab who had planned attacks that killed three Americans overseas, a U.S. official confirmed to Fox News Friday.

Dhoore was riding in a vehicle with two other al-Shabab members Thursday evening when the strike took place about 20 miles south of Jilib in southern Somalia, according to a senior U.S. defense official.

The Pentagon had been watching him off and on for a long time, the senior official adds, saying the Somali government was involved in sharing information that led to this strike.

U.S. officials say Dhoore helped facilitate a deadly Christmas Day 2014 attack at a Somali airport and a March 2015 attack at the Maka Al-Mukarramah Hotel, both in Mogadishu. U.S. citizens were among those killed in the two attacks, the officials said. 

In addition, investigators linked Dhoore to the assassination of a Somali parliament member who also had U.S. citizenship. Dhoore had continued to plot ways to target and kill Americans in the Somali capital, according to the Pentagon.

Dhoore's death, if confirmed, would mark a "significant blow" to the Al Qaeda-linked group and its ability to plan attacks, Pentagon Press Secretary Peter Cook said.

Despite being pushed out of Somalia's major cities and towns, al-Shabab continues to launch deadly guerrilla attacks across the Horn of Africa, and even across the border. The terror group was linked to a 2013 attack on the Westgate Mall in Kenya's capital of Nairobi in which 67 people were killed, as well as an April 2015 attack on Kenya's Garissa University, in which 148 people died.

Fox News' Jennifer Griffin, Lucas Tomlinson and The Associated Press contributed to this report.