A roadside bomb in Yemen's capital Sanaa killed three soldiers and injured two others during a security patrol early on Saturday, a security official said.
The official said the blast targeted a car in Sanaa's al-Hasaba district, a centre of opposition to former Yemeni leader Ali Abdullah Saleh who was ousted early last year.
The official, who requested anonymity, said it was unknown who carried out the attack.
Yemen is the poorest Arab state with a third of the population living on less than $2 a day. It faces a Shi'ite uprising in the north, an Islamist insurgency in the south and east, a southern separatist movement and splits in the military.
Maintaining stability is an important goal for Washington and Gulf Arab countries, which fear the impoverished Arabian Peninsula state could disintegrate, allowing Islamist militants to operate freely.
Yemen, which borders top oil exporter Saudi Arabia and sits along the Red Sea crude shipment route, is already home to Al Qaeda in the Arabian Peninsula.
The country is navigating an uncertain political transition after Arab Spring protests brought down Saleh in early 2012, leading to the creation of a two-year interim government.