Reports from Yemen say President Abed Rabbo Mansour Hadi and his top military commander are on the run while other military leaders, including the defence minister, are under arrest after Shia Houthi fighters entered the southern city of Aden.
The developments came just hours after a television station said Houthi fighters and their allies had seized an airbase where US troops and Europeans helped the country in its fight against al-Qaeda.
The Al-Masirah TV station reported ohat the fighters had "secured'' the al-Annad airbase, and claimed the base had been looted by both al-Qaeda fighters and troops loyal to President Abed Rabbo Mansour Hadi.
Officials loyal to Hadi had no immediate comment.
The US recently evacuated about 100 soldiers, including Special Forces commandos, from the base after al-Qaeda seized a nearby town. The UK also evacuated its soldiers.
The base was crucial in the US drone campaign against al-Qaeda in the Arabian Peninsula.
Hadi, who has fled to the southern port city of Aden, has asked Gulf Arab states to intervene militarily to halt the Houthi advance.
The Shia fighters have already seized Sanaa, the country's capital, and continue to expand their rule in to other regions.
Hadi's foreign minister, Riad Yassin, said Hadi had asked the UN to impose a no-fly zone to prevent the Houthis from using the airbases they hold, calling them a proxy of Iran, a charge the fighters deny.
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.
The six-nation Gulf Cooperation Council - Saudi Arabia, Kuwait, Qatar, UAE, Oman and Bahrain - warned earlier this year that they would act to protect the Arabian Peninsula's security and described the Houthi takeover of parts of Yemen as a "terrorist" act.
Source: Al Jazeera and agencies