WASHINGTON — An American drone strike in Somalia is believed to have killed a key leader of the Shabab militant group, a United States government official said Friday, as the Obama administration continued its intensified air campaign against the group.

First word of the strike came when the Pentagon press secretary, Peter Cook, said in a statement emailed to reporters that the American military, in cooperation with the government of Somalia, was still assessing whether Thursday’s attack had succeeded in killing Hassan Ali Dhoore, described as an important member of the Shabab security and intelligence wing. Defense Department officials said he was involved in two high-profile attacks in Mogadishu more than a year ago in which Americans were killed.

But one United States official, speaking on condition of anonymity to describe initial assessments of the attack, said the military believed that Mr. Dhoore and two others had been killed in the strike, which occurred near Jilib, south of Mogadishu.

In his statement, Mr. Cook said the Shabab leader played a direct role in the Dec. 25, 2014, attack on Mogadishu International Airport, “resulting in the death of several African Union Mission in Somalia personnel and one U.S. citizen.” He said Mr. Dhoore was also “directly responsible” for the March 2015 attack on the Maka al-Mukarram Hotel in Mogadishu, which resulted in the deaths of 15 people, including one Somali-American. Officials said Mr. Dhoore was also involved in the assassination of a dual-citizen member of the Somali Parliament.