Sana’a: Yemen faced a dangerous power vacuum on Friday after its president announced his resignation over a deadly stand-off with militia controlling the capital and lawmakers called an emergency weekend session.

President Abd Rabbo Mansour Hadi, a key US ally in the fight against Al Qaida, said he could no longer stay in office as the country was in “total deadlock”.

“I believe that I have not been able to achieve the goals for which I took up my duties,” he said late on Thursday, adding that Yemen’s political leaders had failed “to lead the country to calmer waters”.

Prime Minister Khalid Bahah also tendered his resignation, saying he did not want to be part of the collapse of the country.

The fall of Hadi’s Western-backed government would raise fears of complete chaos engulfing Yemen, strategically located next to oil giant Saudi Arabia and on the key shipping route from the Suez Canal to the Gulf.

The country is an important power base for Al Qaida in the Arabian Peninsula (AQAP), which claimed responsibility for this month’s deadly attack on French satirical weekly Charlie Hebdo.

Parliament is set to hold an extraordinary meeting to discuss Hadi’s resignation offer, which needs to be approved by lawmakers to take effect.

Hadi adviser Sultan Al Atwani said that parliament would meet on Sunday “at the earliest” because it is in recess and lawmakers need time to return.

Witnesses and security forces said that Al Houthi militiamen had encircled the parliament building overnight, having already seized the presidential palace earlier this week.

Gunmen have also surrounded the houses of top officials including Defence Minister Mahmoud Al Subaihi and head of intelligence Ali Al Ahmadi, a security official said.

Call for protests

The Al Houthis, who hail from Yemen’s northern highlands and who took control of most of the capital in September, said the constitution stipulated that Hadi’s resignation should be approved by an absolute majority in parliament.

“As this has not happened, the resignation remains pending,” the militia said in a statement.

Yemen has been riven by instability since an uprising forced strongman Ali Abdullah Saleh from power in 2012.

Saleh has been accused of backing the Al Houthis.

The Al Houthis, who have long complained of marginalisation, called on supporters to take to the street on Friday afternoon to show their “backing for the revolutionary measures”.

After heavy fighting between government forces and the Al Houthis last week that killed at least 35 people, the UN Security Council and Yemen’s Gulf neighbours had all voiced support for Hadi’s continued rule.

The situation escalated on Saturday when the militiamen seized top presidential aide Ahmad Awad Bin Mubarak in an apparent bid to extract changes to a draft constitution opposed by the Al Houthis because it would divide Yemen into six federal regions.

The Al Houthis continue to hold Mubarak and maintain a tight grip on the capital despite a deal struck late on Wednesday to end what authorities called a coup attempt.

In return for concessions over the disputed draft constitution, the Houthis pledged to vacate the presidential palace, free Mubarak, withdraw from areas surrounding the residences of Hadi and Bahah, and abandon checkpoints across the capital.

Hadi is from Yemen’s formerly independent south and in recent days southern officials have taken steps to back his rule, including closing the air and sea ports in the main city of Aden.

The security and military committee for four of south Yemen’s provinces, including Aden, said in a statement late on Thursday it would not take orders from Sana’a following Hadi’s resignation.

UN Secretary General Ban Ki-moon was “seriously concerned” by the developments and called on all sides “to exercise maximum restraint and maintain peace and stability”, his spokesman said in a statement.

His envoy to Yemen, Moroccan diplomat Jamal Bin Omar, had arrived in the country on Thursday for talks with the political rivals, but they were swiftly overtaken by events.

Oxfam warned that 16 million people — more than half the population — were in need of aid in Yemen.

“A humanitarian crisis of extreme proportions is at risk of unfolding in the country if instability continues,” the aid group said.