SANA, Yemen — Yemen was thrust back into the forefront of the international fight against terrorism Tuesday when the United States and Britain evacuated embassy staff due to a threatened attack, a suspected US drone killed four alleged members of Al Qaeda, and militants shot down a Yemeni Army helicopter.
As Westerners flew out of the country, Yemeni authorities launched an investigation into the Al Qaeda threat to multiple potential targets in the impoverished Arab nation. Security officials said they believed the terror network was seeking retaliation for a US-backed military offensive that has dealt serious setbacks to the terror network’s most active branch, including the death earlier this year of its number two leader.
The Yemeni Army, meanwhile, surrounded foreign installations, government offices, and the airport with tanks and troops in the nation’s capital, Sana, as well as the strategic Bab al-Mandeb straits at the entrance to the Red Sea in the southern Arabian Peninsula, drawing parallels with security measures following the 2000 bombing of the USS Cole in Aden harbor that killed 17 American sailors.
Authorities also set up checkpoints across Sana, searching cars and individuals, especially after night fell. Top government officials, along with military and security commanders, were told to stay vigilant and limit their movements.
Although the immediate threat seemed to be focused on Yemen, the United States has temporarily shut down 19 diplomatic posts in the Middle East and Africa.
A US intelligence official and a Mideast diplomat said that the closures were triggered by the interception of a secret message between Al Qaeda chief Ayman al-Zawahri and Nasser al-Wahishi, the leader of the Yemen-based Al Qaeda in the Arabian Peninsula, about plans for a major terror attack.
The officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly. Zawahri also made a public statement on July 30 that exhorted Muslims to kill Americans ‘‘in every spot on earth.’’
Yemeni investigators looking into the threat said they believe the motive of the attack was retaliation for the killing of Saudi-born Saeed al-Shihri, who was released from the US prison in Guantanamo Bay after nearly six years and later became the number two Al Qaeda leader in Yemen.
Shihri was critically wounded in a November drone strike and later died of his wounds, the militant group acknowledged.
The terror network has had setbacks after the military launched an offensive in June with the help of US forces that has succeeded in uprooting it from strongholds in the south. The group had taken advantage of the instability after the Arab Spring wave of revolutions that led to the resignation of Yemen’s longtime leader Ali Abdullah Saleh.
Yemen’s president, Abdo Rabby Mansour Hadi, met with President Obama at the White House last week, where both leaders cited strong counterterrorism cooperation.
Pentagon spokesman George Little said the US Air Force transported State Department personnel out of Sana early Tuesday. The department said in a travel warning that it had ordered the departure of nonemergency US government personnel ‘‘due to the continued potential for terrorist attacks,’’ adding that US citizens should leave immediately because of an ‘‘extremely high’’ security threat level.
A senior defense official said 50 to 100 diplomatic personnel were flown from Sana in a military transport to Ramstein Air Base in Germany. The official was not authorized to discuss the information publicly and spoke on condition of anonymity. The official said dozens of military troops remain in Yemen, including those providing security at the embassy and others training Yemeni troops.
Britain’s Foreign Office also said it evacuated all staff from its embassy due to increased security concerns. The Foreign Office said the staff were ‘‘temporarily withdrawn to the UK.’’ And the Dutch Foreign Ministry has issued a call for about 40 of its citizens to leave Yemen, although it did not say whether that included its six embassy workers.
Yemen’s government criticized the evacuations in a statement from its embassy in Washington, saying the diplomatic withdrawal ‘‘serves the interests of the extremists and undermines the exceptional cooperation’’ between Yemen and the international community in fighting terrorism. It insisted that its government has taken all precautions to ensure the security of foreign missions in Sana.
Meanwhile, there has been a spike in apparent US drone strikes against Al Qaeda leaders. The attack Tuesday was the fourth in two weeks.
Yemeni officials say the drone fired a missile at a car carrying four men in the al- Arqeen district of Marib province, setting it on fire and killing them. One of the dead was believed to be Saleh Jouti, a senior Al Qaeda member.
In Sana, residents awoke to the sound of an aircraft overhead. Officials said it was American, and photos posted on Instagram appeared to show a P-3 Orion, a manned surveillance aircraft.
The rare overflight of the capital came shortly before the announcements of the evacuations.
The Yemeni military helicopter was shot down by a missile over the Al Qaeda stronghold of Wadi Ubida in central Yemen, officials said. The helicopter was flying from Sana to Marib province, officials said.