"A bus carrying at least 24 air force cadets was blown up on a main road while heading toward the air force base in Sanaa, killing at least 12 cadets," an air force official told Xinhua, saying al-Qaida carried out the attack.
"Initial investigations showed that an intensified explosive device was either planted inside the bus or thrown on the road in front of the bus while it was driving, which totally destroyed it,” the official said, on condition of anonymity.
Security forces have cordoned off the bombing site and sent the wounded to a nearby military hospital.
The official said the wounded were in critical conditions and the death toll might be increased.
Meanwhile, al-Qaida in the Arabian Peninsula (AQAP) claimed responsibility in an exclusive statement received by Xinhua.
"It was the first response from us (AQAP) to Yemeni President Abd-Rabbu Mansour Hadi's remarks, in which he glorified the US drone criminals in Yemen and promised more killings," the statement said.
During a meeting on Thursday in Sanaa, Hadi said that 40 suspected al-Qaida members had been killed in recent counterterrorism operations, and he vowed to keep fighting the Islamists until they laid down their weapons.
"We will force al-Qaida to abandon their arms and considered themselves to be part of the Yemeni people, not an enemy of the people of Yemen," Hadi said.
"AQAP bombed a military cargo plane inside al-Dailamy Air Force in Sanaa in 2012... and it also killed more than 100 soldiers during a rehearsal in the Sabeen Square ... and I will not allow such attacks to be repeated again," Hadi was quoted by the official Saba news agency as saying on Thursday in a graduation ceremony of the police cadets in Sanaa.
"I asked the United States to let our government use drones to fight al-Qaida... drones are more precise in targeting the militants," he said.
A few hours after Hadi made his speech, the AQAP attacked a military post in the southeastern province of Hadramout, killing more than 10 soldiers in suicide attacks on Friday.
The Yemen-based AQAP, which emerged in January 2009, is considered the most strategic threat to the country and its neighboring oil-rich Saudi Arabia.
US drones increased air raid earlier this month against AQAP in Yemen's southern regions after the White House closed the U.S. embassy in Sanaa over security threats. The Yemeni government said more than 40 suspected terrorists were killed in the strikes.
On Sunday, the United States, Britain and Germany reopened their embassies in Yemen after about two weeks of closure.