U.S. airstrikes in Yemen that reportedly killed four al-Qaida commanders Tuesday came hard on the heels of a U.S. Navy SEAL team's Jan. 25 rescue of two Western hostages in Somalia, across the Gulf of Aden.

These U.S. strikes underline how the Americans are escalating covert operations against two Islamist groups in the region -- al-Qaida in the Arabian Peninsula and Somalia's al-Shabaab, which are deemed serious threats to the United States.

Tuesday's attacks in southern Yemen were among the biggest carried out by the Americans in the country at the southern tip of the Arabian Peninsula since airstrikes began there in November 2002 when a drone killed a key jihadist leader.

This is because the attacks, at least three of them, targeted AQAP leaders as part of U.S. President Barack Obama's military doctrine of hitting terrorist organizations with relentless covert operations by Special Forces and the CIA rather than large number of conventional forces.

Among those reported killed in airstrikes by a mix of fighter-bombers and missile-firing unmanned aerial vehicles was Abdel-Monem al-Fathani, a veteran jihadist. Tribal leaders said he was killed with several other al-Qaida members when their two-vehicle convoy east of Lawdar in southern Abyan province was blasted by an unmanned aerial vehicle in a pre-dawn strike.

Fathani allegedly was involved in the suicide bombing of the U.S. Navy destroyer USS Cole Oct. 12, 2000, in Aden harbor in southern Yemen. That attack killed 17 U.S. sailors.

He was also reputedly involved in the March 6, 2002, attack on the 157,000-ton French tanker Limburg off Yemen. In both cases, the bombers rammed explosives-packed small boats into the vessels.

All told, 12-15 AQAP fighters were killed in the recent airstrikes.

These were focused on jihadists operating in southern Yemen, where AQAP and its regional affiliate, Absar al-Sharia, or the Army of Islamic Law, have in recent weeks seized several towns in Abyan and neighboring Shabwa provinces in an offensive that has seriously undermined the crisis-ridden government in Sanaa.

The jihadists have taken advantage of political turmoil in Yemen that has pitted opponents of longtime President Ali Abdullah Saleh against his supporters. The military has split in a yearlong conflict in which hundreds of Yemenis have been killed.

Saleh, who narrowly survived an assassination attempt last summer, has agreed to step down but the political situation remains confused and violence continues.

The conflict impaired the government efforts to confront AQAP, which has become one of the most aggressive and effective al-Qaida affiliates and seeks to establish an Islamic caliphate in Yemen.

U.S. officials say AQAP seeks to join force with al-Shabaab in Somalia to control the strategic Bab el-Mandeb strait at the southern end of the Red Sea, the maritime link between the Mediterranean and the Indian Ocean.

The Abyan towns of Zinjibar, the provincial capital, Al Koud, Ja'ar, Shaqra and Rawdah are held by the jihadists, along with Azzan in Shabwa.

On Jan. 16, AQAP forces led by Tareq al-Dahab, brother-in-law of U.S.-born AQAP ideologue and operational commander Anwar al-Awlaki, seized the town of Rada'a, population 60,000, in Bayhdah province just 100 miles south of Sanaa.

The Americans allege that Awlaki was behind two failed attempts to attack the continental United States, including the Christmas Day 2009 plot to blow up a Northwest Airlines jet over Detroit.

Awlaki, who held U.S. citizenship, was assassinated Sept. 30 in a UAV strike in al-Jawf province. His 16-year-old son, Abdul Rahman, was killed in drone attack Oct. 14.

The Long War Journal Web site, which monitors U.S. operations, says the Americans are known to have carried out 11 airstrikes since May 2011, when Obama intensified the campaign against AQAP. That tally included Tuesday's attacks.

Since December 2009, there have been at least 17 U.S. air or Tomahawk cruise missile strikes against AQAP targets.

One of the most significant developments in recent months is that it's clear the U.S. forces engaged in Yemen, currently headed by the hefty CIA contingent, are operating with far more accurate intelligence than was the case before last year.

On June 3, AQAP's top commanders were hit in one strike and the group confirmed that two important chieftains -- Ali Abdullah Naji al-Harithi and Ammar Abadah Nasser al-Waeli -- were killed.