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The travel warning the State Department issued Tuesday calling on all Americans in the Gulf state of Yemen, including non-essential US government personnel, to leave the country immediately, reflects intercepted Al Qaeda communications urging terrorist actions against Western interests in the country.

But the evacuation of the Americans, including diplomats, may also suggest that the US is planning to intensify the sustained drone war it has been carrying out against Al Qaeda militants in Yemen.

It also reaffirms the view of White House and State Department officials that the Yemen-based Al Qaeda in the Arabian Peninsula (AQAP) is now the terrorist organization鈥檚 most active and dangerous arm.

The travel warning was issued in Washington as the US carried out a drone strike targeting a vehicle traveling north of the capital of Sana鈥檃 and reportedly carrying four Al Qaeda militants, all of whom were killed. Tuesday鈥檚 strike was at least the fourth in the last two weeks 鈥� part of an intensification of the US drone war in Yemen over the past 18 months.

The British government on Tuesday also ordered a drawdown of its diplomatic presence in Yemen.

The Yemeni government lamented the US and British actions in a statement Tuesday afternoon, asserting that 鈥淭he evacuation of embassy staff serves the interests of the extremists and undermines the exceptional cooperation between Yemen and the international alliance against terrorism.鈥�

As if to rebut recent reports of US concerns that Yemen is letting down its guard against Al Qaeda, the statement said Yemen has "taken all necessary precautions" to ensure the security of foreign missions in Sana'a and went on, 鈥淵emen remains strongly committed to the global effort to counter the threats of Al Qaeda and its affiliates.鈥�

The latest US strike followed several others that were carried out just as Yemen鈥檚 recently elected president, Abdrabuh Mansur Hadi, was about to meet last Thursday with President Obama at the White House. Those strikes also reportedly killed a number of militants 鈥� but it is not clear that any of the most recent strikes killed any of AQAP鈥檚 top leaders or most-wanted fighters.

Yemeni officials said one senior AQAP militant, Saleh Jouti, was killed in Tuesday鈥檚 attack, according to the Associated Press, and AQAP confirmed on a website that a July missile strike killed its No. 2 leader, Saeed al-Shehri.

The US travel warning was issued after the US intercepted communications between the head of Al Qaeda, Ayman al-Zawahiri, and Nasir al-Wuhayshi 鈥� the head of AQAP and the man US intelligence believes was recently promoted to be Mr. Zawahiri鈥檚 deputy. In the message, intercepted in the midst of the latest uptick in US drone strikes in Yemen, Mr. Zawahiri is said to tell AQAP to take action urgently against Western interests.

The intensified US focus on Yemen reflects at least in part the Yemeni Al Qaeda affiliate鈥檚 efforts not just to bring down the Yemeni government, but to strike the US on its soil. 鈥淎QAP has a particular track record of trying to attack the American homeland,鈥� says Bruce Riedel, a senior fellow at the Brookings Institution in Washington who advised the last four presidents on terrorism issues.

Several foiled plots of recent years 鈥� the underwear bomber in a plane over Detroit in 2009, the Chicago-bound package bombs of 2010 among them 鈥� emanated from AQAP.

That kind of activity, plus AQAP鈥檚 insurgency against the Yemeni government and its messianic and recruitment activity on the Internet, have drawn US attention and led to redoubled efforts to weaken the organization. US drone strikes in Yemen skyrocketed to 54 last year, compared with 15 in 2011, according to a database kept by Washington鈥檚 New America Foundation.

The database lists 12 drone strikes in Yemen so far this year, not including Tuesday鈥檚 strike.

The US is particularly focused on taking out AQAP鈥檚 notorious bomb maker, Ibrahim al-Asiri, the reputed mastermind behind the underwear bomb and even an unsuccessful 2009 attempt on the life of Saudi Arabia鈥檚 chief counterterrorism official by means of a bomb planted inside Mr. Asiri鈥檚 brother.

The US is anxious to stop Asiri before he develops a bomb that could foil the world鈥檚 best detection systems. But Asiri is also thought to be busy training a workshop full of bomb makers who could replace him if he is killed.

Says Brookings鈥檚 Mr. Riedel, 鈥淗e鈥檚 probably developed a dozen [bomb makers] who could take his place.鈥�