A U.S. Predator unmanned drone armed with a missile sets off from its hangar at Bagram air base on November 27, 2009.

Story highlights

NEW: The bulk of airstrikes in Yemen occurred in the past two years, analyst said

Yemeni troops die in clashes Thursday, security officials say

Another drone strike kills a senior al Qaeda operative over the weekend

Thursday's strikes kill senior leaders of an al Qaeda offshoot, officials say

CNN  — 

A U.S. drone strike killed eight militants in southern Yemen on Thursday morning, the latest hit in an intensified U.S. air camaign against al Qaeda and its affiliates in the area, security officials said.

The attack targeted a convoy carrying senior leaders of the Ansar al-Sharia militant network, an offshoot of al Qaeda, in the Jaar district of Abyan province. The drone strike was followed by a string of air strikes by Yemen’s air force, three security officials said.

Bill Roggio, an analyst on terror and military issues, said 15 U.S. airstrikes this year have targeted al Qaeda entities. Ansar al-Sharia is the political front for al Qaeda in the Arabian Peninsula. He said the bulk of the 32 U.S. airstrikes in Yemen since 2002 have occurred in 2011 and this year.

Suspected al-Qaeda militants seized Abyan last year during Yemen’s political stalemate after government troops evacuated most military posts in the province.

Clashes between government troops and militants also were reported by the security officials Thursday morning in the Abyan districts of Zinjibar, al-Kod and Dofas.

The clashes resulted in the death of three troops in Zinjibar and the injury of six others, local security officials confirmed to CNN.

The developments come less than a week after a senior operative of AQAP was killed by a CIA drone strike and less than three weeks after a terror plot to bring down a U.S.-bound jetliner was foiled.

Fahd al Quso, 37, was killed while riding in a vehicle in the Rafdh district in Shabwa province on Sunday, according to the officials.

Al Quso was indicted by a federal grand jury in New York in 2003 on 50 counts of terrorism offenses for his role in the October 12, 2000, bombing of the USS Cole in Aden, Yemen. The bombing killed 17 U.S. sailors.

The FBI had offered a $5 million reward for any information leading to the capture of al Quso, who was among the most-wanted terrorists in Yemen.

He had been at-large since escaping in April 2003 with eight others from a Yemeni prison, where they had been held on suspicion of involvement in the Cole bombing.

The terror plot revealed this week has been described by U.S. officials as involving a device that is an evolution of the bomb smuggled aboard a U.S.-bound plane on Christmas Day 2009 by a young Nigerian, Umar Farouk AbdulMutallab.

Three months before his death, al Quso foreshadowed the thwarted attack.

“The war didn’t end between us and our enemies,” al Quso told a local journalist. “Wait for what is coming.”

Another high-profile hit occurred in September, when a U.S. drone strike killed Anwar al-Awlaki, an American radical cleric and leading figure in AQAP.

Roggio – managing editor of Long War Journal, a blog providing reporting and analysis on the war on terror – said 32 drone and conventional airstrikes have been used over the decade. All of the strikes this year and four of 10 last year were drone airstrikes.

The airstrike program has had its limitations, Roggio said. He compared it to U.S. operations in Pakistan.

“It’s effective at picking off leaders, but it’s not going to stop AQAP from occupying territory,” he said. Roggio said that militants still control territory in northwestern Pakistan despite the intensification of U.S. drone strikes there since 2008.

Journalist Hakim Almasmari reported from Yemen. CNN’s Joe Sterling reported from Atlanta.