Tribesmen killed five Yemeni soldiers guarding Yemen's strategic Balhaf gas terminal Sunday, two security officials said.
Earlier reports from the officials indicated the attackers were suspected al Qaeda militants, but authorities later said the suspects were not linked to al Qaeda.
The attack took place at a military checkpoint in al-Rowaik district in the southwestern province of Shabwa.
Local security officials told CNN the gunmen escaped unharmed after opening fire on the soldiers from windows of their vehicle. The motive for the attack is not known.
"The attack happened at dawn when soldiers were searching cars passing by. The soldiers were armed but were not able to defend themselves as the attack happened quick and sudden," a security official in the province said.
The official said government authorities are in contact with tribal leaders in the area as they search for the gunmen.
"The next checkpoint was not aware of the attack because all five of the security men were killed before they were able to report it," the added.
This is the first attack on a Shabwa security checkpoint in more than a year. Shabwa has been a stronghold for al-Qaeda for more than two years.
Last week, an airstrike killed five suspected al Qaeda militants in the province, where the Defense Ministry says at least 100 suspected terrorists are hiding.
Four western embassies in Yemen have been closed since August 4, after U.S. intelligence intercepted information that al Qaeda may target American interests in the region.
A senior Defense Ministry official told CNN that 34 people have been killed by 12 drone strikes since July 28.
A heightened security presence has decreased over the last two days in the Yemeni capital of Sanaa. Hundreds of additional troops were deployed after the terror alert on August 3.