Dozens of al-Qaida fighters in Yemen have been reportedly killed in airstrikes, possibly carried out by U.S. forces, sources in the region claim.

The air offensive against al-Qaida in the Arabian Peninsula, the jihadists' branch in Yemen, has intensified as the jihadists, emboldened by political upheaval that threaten to tear the impoverished state apart, mount increasingly large-scale attacks against government troops in the south.

The U.S. administration has been suspected of conducting a secret war against AQIM or al-Shabaab, the Islamist group in Somalia that recently became an al-Qaida affiliate. Knowledgeable sources in Sanaa, Yemen's capital, and in neighboring Saudi Arabia say the recent series of airstrikes in Yemen have been either mounted by U.S. Air Force attack jets or unmanned aerial vehicles operated by the U.S. Special Operations Command or the CIA.

Most of the raids have been carried out from the U.S. counter-terrorism base at Camp Lemmonier, an old French base in Djibouti, a former French colony across the Gulf of Aden from Yemen.

This is the headquarters of the U.S. Combined Joint Task Force--Horn of Africa, established in December 2002 to fight al-Qaida following the 9/11 suicide bombings.

Little is known about the covert operations mounted from there but the Americans reportedly have some 2,000 personnel, including CIA units, there.

The crash of a SOCOM U-28 aircraft in Djibouti confirmed reports that U.S. Special Operations units were deployed at Camp Lemonier, the Long War Journal, which monitors global counter-terrorism operations, reported.

Four U.S. personnel were killed. The rugged and reliable U-28 is the military version of the Swiss-built Pilatus PC-12 single-engine aircraft, which can carry nine men and is considered ideal for covert infiltrations.

SOCOM operates 20 of the turboprop aircraft and has three others on order. The U-28s at Djibouti are believed to have conducted operations in neighboring Somalia, where al-Shabaab is based.

There have been around 30 strikes by U.S. missile-firing Predator and Reaper drones since May 2011 but the tempo has been accelerating with nine attacks this year, including at least five in March.

By comparison there were 10 UAV attacks in Pakistan in that period.

If the reports are correct, al-Qaida has suffered heavy losses from the airstrikes on their camps and government positions they've captured in recent weeks.

Thirty militants were killed in March attacks on Zinjibar, capital of Abyan province, one of several southern towns occupied by al-Qaida.

There have been some key figures among the reported fatalities. One was Abdul Munim Salim al-Fatahani, killed in a Jan. 31 Predator strike near Lawdar in Abyan province, an al-Qaida stronghold in the south, jihadist Web sites said.

Fathani was a veteran jihadist who helped in the suicide attack on the USS Cole, a U.S. Navy destroyer in Aden harbor on Oct. 12, 2000. Seventeen U.S. sailors were killed and the warship was severely damaged.

He also reportedly took part in a similar seaborne attack that damaged the French tanker Limburg in March 2002.

Dozens were reported killed in a pair of airstrikes, possibly by drones, on jihadist bases in the southern towns of Jaar and Al Baydah March 9-10.

The escalation of U.S. operations over the last month appears to have been linked to the Feb. 27 inauguration of Yemen's new president, Abd-Rabbuh Mansir al-Hadi, who replaced longtime dictator Ali Abdullah Saleh.

Saleh, who had ruled since 1978, had been ditched by the Americans after a bloody, yearlong uprising against his regime. He had failed to crush AQAP, which had exploited the political upheaval to make major gains in Yemen.

Hadi, who appeared to be more amenable to U.S. counter-terrorism efforts, pledged no letup in the war against al-Qaida and vowed to retake southern cities and towns they've captured in recent months to set up jihadist rule and undermine Sanaa's authority.

But Hadi's pledges may not mean much. Yemen's military has split, with key units led by Saleh's relatives staying loyal to him.

Under these conditions, with the Americans given greater freedom of action than they had under Saleh, it's to be expected that the supposed "secret war" against AQAP, as well as al-Shabaab in nearby Somalia, will escalate.