Two gunmen on a motorbike killed a Belarussian defence contractor and wounded another as they left a hotel in the Yemeni capital on Tuesday, the former Soviet republic confirmed.

A foreign ministry spokesman in Minsk said Belarussia was still seeking details from the Yemeni authorities but the Russian embassy in Sanaa said the victims of the shooting worked under private contract to the Yemeni army.

"Two citizens of Belarus working in Yemen on private contracts were attacked near the entrance of the Amsterdam hotel in central Sanaa," embassy spokesman Nikolai Lyagushin told Russian's Interfax news agency.

"One of them was killed and the other seriously injured."

Yemeni security sources had initially reported that the two victims were Russian and working as military advisers.

But the Russian embassy said it had no advisers officially seconded to the Yemeni army as military cooperation between the two countries was suspended.

The Yemeni military has instead been relying on private contractors to help maintain its largely Russian- and Chinese-supplied weapons.

Witnesses said the two contractors, both in civilian clothes, were felled by shots to their chests.

They were waiting for two colleagues to come out to share a taxi, hotel manager Mohammed al-Shami said. The four had been staying at the hotel for some four months, he added.

"We heard the shooting. When we rushed out, we found the two in a pool of blood," Shami said.

Two vehicles from the nearby presidential palace arrived around 10 minutes after the attack and took away the casualties and their colleagues.

Yemen's foreign ministry confirmed the attack, saying the "despicable terrorist act" had killed one Belarussian and wounded another.

It vowed to bring the perpetrators to justice.

Hit-and-run assassinations are frequent in Yemen and are mostly blamed on Al-Qaeda militants, or stem from tribal disputes.

Gunmen killed an instructor at the Sanaa police academy, Colonel Ahmed al-Jahdari, on Tuesday, not far from where the foreign contractors were shot, a police source said.

Last week, a member of parliament representing Zaidi Shiite rebels who fought a decade-long insurgency in the far north of Yemen was shot dead in a similar attack.

Abdel Karim Jadban was killed by two attackers on a motorbike as he left a Sanaa mosque.

A German embassy guard was killed last month as he resisted an attempt to kidnap him.

Yemen has been battling through a tough political transition since veteran president Ali Abdullah Saleh was ousted from power in February 2012, following a year of deadly protests against his 33-year rule.

The transition is expected to culminate in a new constitution and pave the way for parliamentary and presidential elections in February 2014, but it faces many hurdles.

There are growing demands for the secession of the formerly independent south, while there is still on-off fighting in the far north between the Shiite rebels and hardline Sunnis.

The rebels bombarded the Sunni hardliners' base in Dammaj on Tuesday, killing the son of one of their leaders, Abdel Rahman Yahia al-Juburi, sources in the town said.

Yemen is also battling against Al-Qaeda in the Arabian Peninsula, which is regarded by Washington as the jihadist network's most dangerous branch.

AQAP fighters carry out frequent attacks in the south and east, despite a major army offensive last year and repeated US drone strikes targeting its commanders.