The strike follows Yemen's announcement on Wednesday that it had foiled a plot by al-Qaeda to seize two major oil and gas export terminals and a provincial capital in the east of the country.
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The drone killings also come after warnings of potential attacks by militants that pushed Washington to shut missions across the Middle East, and the United States and Britain to evacuate staff from Yemen.
Witnesses and local officials in Maareb, a mostly desert region where militants have taken refuge, said the drone fired at two vehicles suspected of carrying al-Qaeda operatives at dawn, killing six people.
Residents saw the two vehicles rise in flames and the drones circled the air for a while after the attack.
At least 20 suspected operatives have been killed since July 28, when a drone strike killed at least four members of Ansar al-Sharia, a local militant group affiliated with al-Qaeda in the Arabian Peninsula (AQAP), one of the most active branches of the network founded by Osama bin Laden.
Yemen, one of the poorest Arab countries, is one of a handful of countries where Washington acknowledges targeting militants with strikes by drone aircraft, although it does not comment publicly on the practice.
US sources have told Reuters that intercepted communication between bin Laden's successor as al-Qaeda leader, Ayman al-Zawahri, and the Yemen-based wing was one part of the intelligence behind the alert last week that prompted the closure of the embassies.
Security in Yemen is a global concern. Home to AQAP, considered one of the most aggressive branches of the global militant organization, it shares a long border with Saudi Arabia, a US ally and the world's top oil exporter.
The US government supports Yemeni forces with funds and logistical support.
Yemeni authorities issued a statement early on Tuesday listing 25 "most wanted terrorists" it said were planning to carry out attacks in the country during the Muslim Eid al-Fitr holiday which starts Thursday. They also offered a five million Yemeni riyals ($23,000) bounty for information leading to their capture.
Qaeda leadership
Al-Qaeda's core leadership remains a potent threat, and experts say it has encouraged the terror network's spread into more countries today than it was operating in immediately after the September 11, 2001, terrorist attacks.
Osama bin Laden's replacement, Ayman al-Zawahri, an Egyptian whose location is unknown, issues messages to followers every few months that are posted and circulated on jihadi websites.
His latest, posted July 30, criticized US President Barack Obama for the continued US detention of terror suspects at Guantanamo Bay, Cuba, and for launching deadly drone attacks in Pakistan, Afghanistan, Yemen and other Muslim countries.
"You fought us for 13 years. ... Did we soften or toughen up? Did we back out or advance? Did we withdraw or spread out?" al-Zawahri asked Obama in his message, according to a transcript of his letter that was translated from Arabic by SITE Intelligence Group, which monitors jihadist websites.
He continued, "I call on every Muslim in every spot on Earth to seek with all that he can to stop the crimes of America and its allies against the Muslims – in Palestine, Iraq, Afghanistan, Yemen and Mali, and everywhere."
Three days later, the State Department announced the temporary closing of US embassies and diplomatic outposts – although not in Iraq, Afghanistan, Israel or Mali.
Officials this week said the closures were prompted by an unspecified threat to US and Western interests in a message from al-Zawahri to his top lieutenant in Yemen, where al-Qaeda in the Arabian Peninsula is based.
AQAP, as the terror network's regional hub is known, is led by Nasser al-Wahishi, who for years was close to al-Zawahri and bin Laden and is one of al-Qaeda's few remaining core leaders, said SITE director Rita Katz.
Intelligence officials say AQAP has for years announced its intent to attack the US, and it is widely considered the biggest threat to the West of the al-Qaeda affiliates.
Al-Qaeda Organization in the Islamic Maghreb is rooted in Algeria and affiliated with al-Zawahri, who in April warned French troops fighting extremists in Mali that they would face "the same fate America met in Iraq and Afghanistan" as long as they stayed. But there's no evidence the North African groups receive direct orders from al-Zawahri, and most are as motivated by criminal activity as by anti-Western ideology.
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