State media has blamed fighting in the south, in which dozens have been killed in the past three months, on Al Qaeda’s resurgent regional wing and armed separatist militants.
The attack on the checkpoint occurred in Zinjibar, capital of the flashpoint Abyan province.
Al Qaeda’s wing previously focused on high-profile strikes on foreign targets but has started to aim at the state in response to enhanced U.S.-Yemeni cooperation in a crackdown against the group that has included air strikes and raids.
In the capital Sanaa, authorities arrested three Al Qaeda members who were preparing attacks, an official said.
Security measures were stepped up at key installations during a crackdown on militants, the Interior Ministry said.
The US embassy said on its website this week that it was suspending non-essential travel outside Sanaa for its staff because of ‘continuing threats from Al Qaeda in the Arabian Peninsula (AQAP) and its affiliates’.
Yemen surged to the forefront of Western security concerns when AQAP claimed responsibility for the failed bombing of a U.S.-bound plane in December.
The impoverished Arabian Peninsula country, also struggling with rebels in the north, is under international pressure to quell domestic conflicts and focus on the Al Qaeda wing.
Western powers and neighbouring top oil exporter Saudi Arabia fear Al Qaeda is exploiting instability in Yemen to use it as a launch-pad for attacks regionally and beyond.
US officials said this week Washington would likely step up strikes against Al Qaeda in Yemen, seeking to apply the same degree of pressure there as covert drone attacks in Pakistan have had on the core group.
But Sanaa rejected an increased US role in the fight against Al Qaeda.
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