Washington: With the killing of Saudi-born Abu Hafs al-Shahri, al-Qaeda's operations chief in Pakistan, the US says it has removed a "key threat" in the war against terrorism in Pakistan's lawless tribal areas, dubbed as the "epicenter" of the world's jihadists.

Al-Shahri was killed in Pakistan's tribal belt earlier this week, less than a month after the killing of Atiyah Abdul Rahman, al-Qaeda's no. 2 man there.

Al-Shahri was seen as a possible successor to Rahman, who was killed in late August in Pakistan, a US official was quoted as saying.

As al-Qaeda's Pakistan operations chief, one official said, al-Shahri's responsibilities included coordinating the activities of the outfit's depleted central leadership with Pakistani Taliban (TTP).

"This is another blow at the core of al-Qaeda in Pakistan," a US official said, adding that his death "removes a key threat inside Pakistan."

Al-Shahri "was reputed to have become particularly adept at devising methods to cause additional harm, such as suggesting ways to the Taliban of making bombs more effective," CBS News quoted a defence official from a NATO member country based in Islamabad as saying.

The NATO official said news of al-Shahri's death was seen by defence officials in western countries, including the United States, as "a major step forward. People are excited."

Al-Shahri's death is the latest in a series of losses among the top ranks of the terrorist network since the covert US commando raid that killed its founder, Osama bin Laden, in Abbottabad on May 2.

In addition to Abdul Rahman's death, Pakistan's military announced the arrest of a senior al-Qaeda operative Younis al -Mauritani in the Quetta area on September 5.

Though days have passed since al-Shahri was killed, it is still unclear how he was eliminated. However, the CIA has been using armed drones to target militants in the tribal region.

A Pakistani intelligence official based in North Waziristan said he suspected, but could not confirm, that al-Shahri was killed in a drone strike on September 11, the Washington Post reported. "Pakistan's Federally Administered Tribal Areas (FATA) remain the epicentre —- the 'Star Wars Bar,' if you will – of the world's worst of global 'jihad'," Michael Vickers, the
Under Secretary of Defence for Intelligence, said this week at the National Defence University.

Pressure on al-Qaeda, driven mainly by the CIA's drone campaign, has wiped out a handful of al-Qaeda's top leaders over the past several months, forcing the group to promote members who were relatively unknown into positions of leadership, the Post noted.

Al-Shahri was far less notorious than Abd al-Rahman, but was seen as a "contender to assume some of Atiyah's duties," a second US official told the paper.

The rise of Shahri, who was little-known, illustrates the rate of promotion within al-Qeada as the CIA's drone campaign continues to pick off senior leaders.

"They are not having the period of apprenticeship they had in the past, which may be one reason why they are getting nailed faster," said Bruce Hoffman, a counter-terrorism expert at Georgetown University.

"The people still out there have to be convinced their time is near and are spending more time thinking about that than planning operations; it realigns their priorities from attacks to survival," Hoffman said.

US officials have said that al-Qaeda's core now poses less of a threat to the United States than some of its affiliates and associated movements, primarily in Yemen, Somalia and North Africa.