Sana’a, Asharq Al-Awsat—Saudi Border Guard forces across the Kingdom’s southern border with Yemen have been placed on high alert after Houthi fighters took control of a key government border post on Thursday.

Houthi rebels in control of as many as nine Yemeni provinces have continued their push across the country, raising fears in neighboring Saudi Arabia. Militants affiliated with the Shi’ite Houthi movement on Thursday captured the border town of Harad between Saudi Arabia and Yemen, sources who spoke on the condition of anonymity told Asharq Al-Awsat. Harad is located in Yemen’s northern Hajjah governorate and contains the strategically-important Tawwal border post which allows the transfer of people and goods between the two countries.

Saudi Border Guard spokesman Gen. Mohamed Al-Ghamdi informed Asharq Al-Awsat that security forces positioned on the Kingdom’s northern and southern border have been placed on full alert. Saudi Arabia’s Border Guard are carrying out round-the-clock checks for cross-border violations, including drug-trafficking, weapon smuggling and infiltration by terror groups.

No illegal cross-border activities were recorded as of Thursday evening, the official said, adding that patrols are combing the Saudi side of the border as part of a wider campaign to tighten security in the area.

Ever since Houthis took control of large parts of the country last month, Yemen has witnessed an unprecedented surge in violence amid fears of a sectarian civil war breaking out in the country.

Al-Qaeda militants on Wednesday took control of government bases in the Al-Adeen area in Ibb province, 120 miles south of Sana’a, killing and injuring a number of security officers.

“Four cars carrying dozens of Al-Qaeda militants attacked the city, killing more than three soldiers and injuring six others,” a local source who spoke on the condition of anonymity told Asharq Al-Awsat.

Ansar Al-Sharia, a group affiliated to Al-Qaeda in Yemen, claimed responsibility for the attack in a statement on its Twitter account, maintaining that the operation had foiled a government plot to hand the city to the Houthis.

On Tuesday Houthi militants were deployed across the city, setting up checkpoints without any resistance from government forces.

For its part, sources close to Yemen’s presidency denied facilitating the Houthi expansion across the country.

Speaking to Asharq Al-Awsat on the condition of anonymity because he was not authorized to brief the media, a presidential source said: “The presidential establishment is facing a number of problems due to the expansion of Houthis, the spread of Al-Qaeda and the growing activities of the [secessionist] Hirakmovement in the south.”

“President Abd Rabbuh Mansur Hadi is making every effort to preserve the unity of Yemen in light of the present circumstances,” the source added.

The Houthis swift expansion across Yemen with little or no government resistance has threatened to ignite sectarian tensions after radical Sunni militants responded by stepping up attacks on Shi’ite targets.

Elsewhere, Houthis militias exchanged gunfire with Al-Qaeda fighters in the central Baydah province after several Shi’ite militants on their way to the Rada’ district were killed in an ambush.

Violent clashes raged between Al-Qaeda and Houthi insurgents north of Rada’ district after radical Sunni militants ambushed a group of Shi’ite fighters, senior tribal Shiekh Ali Saleh Abu Srima told Asharq Al-Awsat.

The Gulf Cooperation Council (GCC) expressed concern over the growing turmoil in Yemen as member states called for the reinstatement of the authority of the central government in Sana’a.

Speaking to Asharq Al-Awsat on the condition of anonymity, a senior official within the GCC diplomatic mission to Yemen affirmed that Gulf states are closely monitoring “the unfolding situation in Yemen, including the Houthis expansion in several provinces.”

“The GCC will not accept Yemen becoming a failed state,” the official added.

Hamdan Al-Rahbi contributed reporting from Sana’a. Nasser Al-Haqbani contributed reporting from Riyadh.