The assassination of one of Yemen's top military commanders, presumably by al-Qaida in retaliation for a government offensive, suggests the organization is far from crushed despite growing U.S. involvement in the conflict.

And there's another ominous sign: the suicide bomber who killed Maj. Gen. Mohammed Salem Ali Qatan in the southern port city of Aden Monday was reported to be a Somali.

If that is the case, it suggests that the al-Shabaab Islamist group in Somalia may have a tighter relationship with al-Qaida in the Arabian Peninsula, the jihadist group in Yemen, than was previously thought.

U.S. intelligence has been claiming for some months that there have been moves by the two groups, separated by the Gulf of Aden, to join forces. Their apparent aim is to control southern Yemen to dominate the Bab el-Mandeb Strait, the oil artery that links the Red Sea and the Indian Ocean.

But al-Qaida and a substantial group within al-Shabaab want to attack the United States. AQAP has made three unsuccessful attempts to bomb U.S. aircraft.

What makes al-Shabaab so attractive to AQAP is that its so-called "foreign wing" includes Somalia-born U.S., British and European citizens who would be able to infiltrate Western societies with little difficulty to carry out attacks.

On April 19, 2011, U.S. forces captured Ahmed Abdulkadir Warsame, an al-Shabaab operative with close ties to AQAP in Yemen, as he was traveling in a fishing boat in international waters from Yemen to Somalia.

He was reportedly held incommunicado in the brig of the U.S. Navy amphibious ship USS Boxer in the Arabian Sea for two months for in-depth interrogation before he was taken to New York.

He was indicted June 30, and formally "arrested" on July 3 on charges of seeking to broker an arms deal between AQAP and al-Shabaab.

The Warsame episode marked a significant shift in how terrorism suspects are handled following capture and this could point to wider use of such tactics known only to U.S. intelligence and the White House in line with U.S. President Barack Obama's escalation of the war against the jihadists from North Africa to Yemen and Pakistan.

Qatan led the Yemeni military's campaign, backed by U.S. airstrikes, against al-Qaida and was also the theater commander for southern Yemen.

The Defense Ministry version says he was killed with two aides when the suicide bomber threw himself on the hood of the general's vehicle and detonated explosives strapped to his body.

Another account says Qatan was walking into his headquarters in Aden, when the bomber stopped him, shook his hand and then detonated his bomb.

The assassination, the first against such a high-ranking Yemeni officer, took place as al-Qaida pulled out of the coastal town of Shuqra in southern Al-Abyan province, a longtime jihadist stronghold as the army swept in.

Shuqra was the third al-Qaida bastion to fall in a week after the cities of Jaar and Zinjibar, the provincial capital and a symbol of al-Qaida's successes in recent months.

The towns were seized in 2011 as the Sanaa government struggled to restore control after a yearlong uprising that resulted in longtime dictator Ali Abdullah Saleh stepping down.

The military splintered with some units remaining loyal to Saleh and his relatives who still command major formations, while others stood behind Saleh's successor and longtime deputy, Gen. Abdu Rabbo Mansour Hadi, pushed into office in February by the Americans.

Qatan was the highest-ranking officer killed since Yemen, ancestral home of the late Osama bin Laden, became embroiled in the war against al-Qaida's death two decades ago.

The broad-daylight assassination was a major setback for the military operation against al-Qaida that began May 12 and which by military count has killed nearly 600 jihadists.

But it's too soon to determine whether it will undermine that campaign as it was finally getting to grips with the jihadists and their local ally, Ansar al-Sharia, or Partisans of Islamic Law.

Al-Qaida has been reported to be under intense pressure around Azzan, in neighboring Shabwa province as it tried to regroup and rearm.