Unknown gunmen fired two rocket-propelled grenades at a military patrol in Yemen's southern port city of Aden early on Wednesday, injuring at least two army personnel, officials said.

"The military patrol team came under terrorist attack by masked gunmen who fired rockets on the soldiers' vehicle and they responded with gunfire," local officials said.

The incident happened near a public square of the pro-secession southern movement in Aden's neighborhood of Mansora. It's still not clear if anyone of gunmen was hurt.

The armed forces and police combed the area in search for the perpetrators, local residents said.

An armed faction of the secessionist movement was believed to be behind the operation, according to Yemeni officials.

North and South Yemen unified peacefully in 1990, but their relationship deteriorated in 1994. Calls for separation in the country's southern regions were renewed in 2007.

Southerners have been complaining of being marginalized, particularly since they lost a four-month civil war in 1994.

Pro-secession protests are on the rise in the south amid a worsening economic situation and allegations of discrimination in favor of the northerners.

Concerns have increased since the conflicts in south Yemen are creating instability where al-Qaida could gain foothold.