Yemen's Houthi rebels have advanced towards Aden, where President Abd-Rabbu Mansour Hadi has been holed up since fleeing the capital Sanaa last month.

Before moving closer to the coastal city on Wednesday, rebels seized an airbase that until a few days ago was used by US troops deployed in the fight against al-Qaeda. 

The al-Anad base, 60km from Aden, had since been occupied by Yemeni government forces. 

The advance of the Houthis threatens to plunge the Arab world's poorest country into a civil war that could draw in its Gulf neighbours. Already, Hadi has asked the UN to authorise a foreign military intervention in the country.

Yemeni Foreign Minister Ryiad Yassin repeated the call for military action in an interview with Al Jazeera on Wednesday.

"We want direct military intervention, especially by air force, to stop the advance of Houthis on the ground," Yassin said in Sharm el-Sheikh, Egypt. He also dismissed attempts to reach a solution to Yemen's crisis through dialogue, alleging that UN envoy Jamal Benomar had given "legitimacy to the Houthi coup".

Hadi established a temporary capital in Aden after fleeing from house arrest at the hands of the rebels in Sanaa earlier in March.

The Shia rebels, who say they are fighting for more rights for their Zaidi community, have taken over large parts of Yemen since last year.

Airport closed

As the situation in Aden escalated on Wednesday, the city's airport was shut down due to security concerns. Sources told Al Jazeera that Brigade 39, loyal to overthrown President Ali Abdallah Saleh and allied with the Houthis, took control of the airport, leading to suspension of flights there.

There were conflicting reports on Hadi's whereabouts as witnesses said gunfire was heard close to his residence.

Witnesses speaking to the Associated Press said they saw a convoy of presidential vehicles leaving Hadi's palace, located at the top of a hill in Aden overlooking the Arabian Sea.

Presidential officials speaking to the news agency said Hadi was in an operations room overseeing his forces' response to the Houthi offensive but declined to say where that facility is located. 

Other reports sugegsted Hadi had left the city by boat.

In Sanaa, Yemen's state TV, now controlled by the Houthis, made an offer of nearly $100,000 for Hadi's capture.

Summer Nasser, a human rights activist speaking to Al Jazeera from Aden, said Hadi "left his compound but we do not know where he is".

"There are gun shots close to the compound, but we cannot confirm who is fighting who or if there are Houthis troops on the ground there," she said.

"There have been military jets patrolling around the compound," she said.

Meanwhile, Houthis said that their forces captured Defence Minister Mahmud al-Subaihi as they advanced towards Aden. 

"Subaihi was arrested in the city of Houta" in Lahij province, rebel spokesman Mohammed Abdulsalam said in a statement aired by their Al-Massira television.

Al Jazeera could not independently verify the report.

Diplomatic missions of Hadi's Arab Gulf allies, including Saudi Arabia, UAE and Kuwait, have evacuated their diplomatic staff from Aden over the past few days, officials said.

They earlier evacuated from Sanaa and relocated to Aden to support Hadi.

Saud Al Faisal, Saudi Arabia's foreign minister, has warned that his country would take "necessary measures" if the Houthis did not resolve the crisis peacefully, without elaborating further.

Al Jazeera