(CNN) -- Gunmen on a motorbike killed a Russian military instructor and wounded a second Tuesday in Yemen's capital of Sanaa, two senior police officials said.
They used silencers and needed only seconds for the attack, eyewitnesses said.
"We only realized when the two Russians were on the floor and a motorcycle was seen escaping the scene," said Saleh al-Matari. "They escaped by using side streets and driving through residential areas."
Security forces arrived 10 minutes later, witnesses said. The wounded man was taken to a hospital, according to police.
The two victims were advising Yemen's army as private security contractors, said the police officials, who spoke on condition of anonymity. They were walking out of their hotel when they were shot.
The Russian Embassy would not confirm that the victims were Russian.
Last month, a German security expert was shot dead as he walked out of a Sanaa supermarket.
Yemen is the most impoverished country in the Middle East and is plagued by two major bloody conflicts.
Shiite Houthi rebels have fought a separatist battle for years but recently came to a cease-fire agreement with the government of the majority Sunni nation. Last week, one of their representatives in Yemen's parliament was shot dead by gunmen on a motorcycle in Sanaa.
Yemen is also a home to al Qaeda in the Arabian Peninsula, which many analysts believe is the most dangerous wing of the terrorist network. U.S. counterterrorism officials have said that AQAP strives to attack targets outside of Yemen.
With the help of drone strikes allegedly carried out by the CIA, Yemen's military put militants in the country's tribal region on retreat last year, but AQAP regularly carries out terrorist attacks on soldiers and officials.