At least one person has been killed and dozens injured in a bomb attack on a bus carrying Yemeni air force officers in Sanaa.
Al Jazeera's Hashem Ahelbarra, reporting from the Yemeni capital, said the bus was on its way to Sanaa airport when Sunday's bombing occurred.
"The attack comes against a backdrop of heightened security in the capital amid concerns ... that al-Qaeda could launch an attack," he said.
Sanaa International Airport is adjacent to a base which has been used by the Yemeni air force.
There were no indications as to whether the blast was a suicide attack or a bomb planted inside the bus.
The Yemeni government is battling fighters linked to al-Qaeda across the country.
Yemeni security forces described Sunday's blast as a "terrorist attack" - a hint which means Al-Qaeda in the Arabian Peninsula (AQAP) could be involved.
The Yemen-based AQAP is al-Qaeda's most active franchise, having been behind numerous attacks on the country's security forces.
The attack in Sanaa comes two days after a speech of Abd-Rabbu Mansour Hadi, Yemen's president, where he said his country and the US were coordinating efforts to combat AQAP and pledged to defeat them.
The US closed 19 of its consulates and embassies in Arab and Muslim countries, including Yemen, amid what American officials said was a threat of an imminent al-Qaeda attack three weeks ago.
It finally reopened the embassy in Sanaa on Tuesday although other missions had already reopened.
Britain and France had also shut their embassies in Yemen but they later reopened the offices.
Hadi said on Friday that a pledge made by Nasser al-Wuhayshi, AQAP's head, to Ayman al-Zawahiri, al-Qaeda's chief, to "change the course of history" had led to the closure of Western embassies in the country.
Yemen has been in turmoil since pro-democracy protests against the former President Ali Abdullah Saleh broke out in early 2011.
Attacks against military personnel are more common in the mainly lawless south and east where an insurgency is still raging.