The death of Fahd al Quso, a senior al Qaeda figure in Yemen, comes as the Yemeni military and the CIA step up their campaigns to degrade what's often called al Qaeda's most dangerous affiliate.
Al Quso, 37, was killed in a drone strike Sunday in a remote part of one of Yemen's most lawless provinces.
His "martydom," along with the death of another unnamed militant, was confirmed by al Qaeda in the Arabian Peninsula (AQAP).
Al Quso is the most prominent casualty yet of an offensive against al Qaeda ordered by Yemen's new President Abdu Rabu Mansour Hadi and supported by a broader U.S. drone campaign.
U.S. officials said that in late April, the CIA and the U.S. military received authorization to launch strikes in Yemen even when the target's identity was not confirmed.
Al Quso's death could not have come at a better time for Hadi.
On Saturday, he told graduates at Yemen's Military Academy that "the real battle against the terrorist al Qaeda organization has yet to begin and will not end until we have eradicated their presence in every district, village and position."
Diplomatic sources say Hadi has proved much more assertive than his predecessor Ali Abdullah Saleh in taking the fight to al Qaeda.
FBI Director Robert Mueller visited Yemen last month to discuss the counter-terrorism program. A presidential aide subsequently told CNN that Hadi had promised complete cooperation with the United States in the battle to uproot al Qaeda.
The last few weeks have seen daily clashes and air-strikes against al Qaeda militants and their allies in the southern provinces of Shabwa and Abyan.
A U.S. drone hit an al Qaeda training site Wednesday near the town of Jaar, killing 13 suspected militants, according to Yemeni security officials.
And in Marib, further north, a senior AQAP commander, Mohammed Saeed Al-Umda, was killed when an airstrike targeted a militant convoy on April 22.
Al-Umda had been a bodyguard to Osama bin Laden, according to an AQAP statement acknowledging his death.
A statement from Yemen's embassy announcing Al Quso's death did not specify that he was killed by a U.S. missile strike -- perhaps because of sensitivity about foreign operations on Yemeni territory. But he was the most significant al Qaeda casualty in Yemen since militant preacher Anwar al Awlaki was killed in a drone strike in September.
Al-Quso was on the FBI's most wanted list, with a $5 million reward for information leading to his capture. He was indicted in the United States for his role in the bombing of the USS Cole in the Aden, Yemen's main port, in 2000. But the Saleh government released him from prison in 2007.
According to a CNN tally, there have been at least 15 drone strikes against militant targets in Yemen so far this year.
But the escalated campaign risks a backlash among tribes in southern Yemen that have accommodated al Qaeda and its ally Ansar al-Shariah, and the thousands of civilians whose homes have been destroyed and livelihoods ruined.
Yemen scholar Gregory Johnsen wrote recently on his blog that "too often in Yemen drones have been a shortcut that bypasses the really difficult work of diplomacy and counterterrorism."
Johnsen, a professor at Princeton University, added that "drones seduce us with their ability to kill bad guys without putting U.S. troops at risk. But this war isn't about killing bad guys; it's about defeating al Qaeda."
White House counterterrorism adviser John Brennan described AQAP as "very, very dangerous" in a speech in New York last month. He said AQAP had more than 1,000 members in Yemen and "close connections" to al-Qaeda leadership in Pakistan.
The Yemen affiliate has been behind two of the most audacious attempts to target the United States in recent years -- including the so-called "underpants" bomb aboard a Christmas Day flight to Detroit in 2009, and the printer bombs loaded onto cargo planes in 2010 and destined for an address in Chicago.
Turning the tide against AQAP, as President Hadi acknowledged, is likely to be a long slog.
In early March, al Qaeda fighters overran a military base in Zinjibar, the capital of Abyan province, capturing more than 100 soldiers and military equipment. The majority of the captives were freed only last week. Another attack on the outskirts of Aden left ozens of poorly-equipped soldiers dead.
AQAP has also declared "Islamic emirates" in three areas, setting up Shariah courts and attempting to provide basic services.
The towns of Jaar and parts of Zinjibar are still held by militants. Jaar has been heavily shelled in the last month, as have militant positions around the town of Lowder, where local people said they had formed militia to join the fight against the militants.