Meanwhile, there has been a spike in apparent U.S. drone strikes against al-Qaida 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-Qaida member.
In Sanaa, 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-Qaida stronghold of Wadi Ubida in central Yemen, officials said. The helicopter was flying from Sanaa to Marib province, officials said. The eight who were killed, including a military commander, were part of a military force guarding oil installations in the province.
The Yemeni officials who provided the information on the suspected drone, the helicopter downing and the security in the capital all spoke on condition of anonymity because they were not authorized to talk to the media.
Yemeni authorities also released the names of 25 wanted al-Qaida suspects Monday, saying they were planning terrorist attacks in Sanaa and other cities.
Officials say potential U.S. targets in Sanaa could include the embassy and other buildings used by the United States to house personnel, as well as a military facility a few kilometers (miles) outside used by U.S. aircraft.
The government statement said security forces will pay $23,000 to anyone coming forward with information leading to the arrest of any of the wanted men. Among them are alleged senior figures in al-Qaida’s Yemen branch, including Saudi nationals Ibrahim Mohammed el-Rubaish and Ibrahim Hassan el-Assiri.
El-Rubaish was released from Guantanamo in 2006 and is believed to have played significant roles in al-Qaida’s expanding offshoot in Yemen. He is a theological adviser to the group and his writings and sermons are prominent in its literature.
Military officials said the threat may be related to the Bab al-Mandeb, pointing to a visit Sunday by the defense minister, Gen. Mohammed Nasser Ahmed, to Yemeni forces positioned at the Red Sea entrance about 276 kilometers (170 miles) south of Sanaa.
Officials said the visit came after they received intelligence that al-Qaida could be targeting foreign or Yemeni interests at the vital maritime corridor, a main thoroughfare for international shipping but also a crossing point for smuggled weapons and illegal immigrants between east Africa and Yemen.
Ahmed urged the forces to stay ‘‘on alert against any sabotage operations aiming at destabilizing the country,’’ according to the officials. They also spoke on condition of anonymity because they were not authorized to talk to the press.
Yemen, a decentralized and predominantly Muslim country that is the ancestral homeland of the late al-Qaida leader, Osama bin Laden, has been the site of numerous anti-U.S. plots and attacks.
Besides the strike against the USS Cole, al-Qaida attacked the U.S. Embassy in Sanaa in 2008, killing one American. Western embassies were locked up in 2010, days after the foiled plot on Christmas Day in which a passenger on a Detroit-bound plane allegedly tried to detonate explosives in his underwear. The Obama administration said the suspect was trained and armed by the al-Qaida affiliate in Yemen.
Washington considers the al-Qaida branch in Yemen to be among the terrorist network’s most dangerous. The United States has also assisted Yemen in fighting the militants who, at one point in the country’s recent turmoil, had overrun large sections of the south. The group has also carried out bold attacks on Yemeni security forces, killing hundreds in the past two years.
A Yemeni security council met later Tuesday to discuss security leaks, according to an official with knowledge of the meeting. Council members concluded that government officials had passed on information to al-Qaida under Saleh’s rule and that some of those leaks continued even after Hadi took over, said the official, speaking on condition of anonymity to discuss the meeting.
Lee reported from Washington. Associated Press writers Maggie Michael in Cairo and Lolita C. Baldor and Deb Riechmann in Washington contributed to this report.