Al-Qaida planned to target the cities of Mukalla and Bawzeer, then send militants disguised as Yemeni troops to attack two strategic oil ports in the impoverished country on the Arabian Peninsula, government spokesman Rageh Badi said.
Other al-Qaida militants would also try to sabotage pipelines to "create panic among Yemeni army and Yemeni security services," Badi told The Associated Press, adding that authorities managed to foil the plots in the past 48 hours.
Details of the plot were first reported by the BBC.
His remarks came hours after Washington apparently stepped up its drone strikes in Yemen in the covert fight against militants from al-Qaida's branch, which is considered the most active of the terrorist network.
Security officials and residents said early Wednesday that a suspected U.S. drone strike killed seven suspected al-Qaida militants in southern Yemen, the fifth such attack in the country in less than two weeks.
Yemen has emerged as the focus of a feared attack that has led the U.S. to shut down temporarily 19 diplomatic posts in the Middle East and Africa. American and British workers from embassies in Yemen's capital of Sanaa also have been evacuated.
Washington has been backing a campaign by Yemen's military to uproot al-Qaida militants and their radical allies who had taken over a string of southern cities and towns. The militants have largely been driven into the mountains and countryside, and Yemeni intelligence officials say the current threat may be retaliation for that offensive.
A U.S. intelligence official and a Mideast diplomat told the AP that the closures were triggered by the interception of a secret message between al-Qaida chief Ayman al-Zawahri and Nasser al-Wahishi, the leader of the Yemen-based al-Qaida in the Arabian Peninsula, about plans for a major attack.
The drone strike killed the militants in Shabwa province, setting two vehicles on fire, security officials said. All the officials spoke on condition of anonymity because they were not authorized to discuss the matter with the media.
Residents of the Markha region of Shabwa province said they saw several bodies in two burning cars. The residents spoke on condition of anonymity because they feared retaliation.
While the United States acknowledges its drone program in Yemen, it does not confirm individual strikes or release information on how many have been carried out.
An AP reporter in Sanaa said a drone buzzed over the capital for most of the day.
Security checkpoints have been set up across Sanaa, searching cars and individuals. The Yemeni army has surrounded foreign installations, government offices and the airport with tanks and troops in the capital as well as the strategic Bab al-Mandeb straits at the entrance to the Red Sea in the southern Arabian Peninsula. Top government officials, along with military and security commanders, were told to stay vigilant and limit their movements.
The terrorist network's Yemeni offshoot, known as al-Qaida in the Arabian Peninsula, has been bolstering its operations for the past few years after key Saudi operatives fled there following a major crackdown in their homeland.
The group overran entire towns and villages in 2011, taking advantage of a security lapse during nationwide protests that eventually ousted Yemen's longtime ruler, Ali Abdullah Saleh. Backed by the U.S. military, Yemen's army was able to regain control of the southern region, but al-Qaida militants continue to launch deadly attacks on security forces.