Yemeni President Abd-Rabbu Mansour Hadi accused the Iranian-allied Houthi militia on Saturday of staging a coup against him and appealed to the United Nations for "urgent intervention", even as the United States evacuated its remaining forces.
In a call to arms from the southern city of Aden, where he fled last month after escaping house arrest by the Houthis, Hadi called on them to pull their forces out of state ministries, return weapons seized from the army and quit the capital, Sanaa.
The UN Security Council was set to meet on Sunday to discuss Yemen after Hadi appealed to the 15-member body for assistance "in all available means to stop this aggression".
Yemen has been hurtling towards civil war since last year when the Houthis seized Sanaa and advanced into Sunni Muslim areas, leading to clashes with local tribes and energizing a southern separatist movement.
US officials said Washington had evacuated its remaining personnel from Yemen, including about 100 special operations forces, because of deteriorating security, marking a further setback in US efforts against a powerful local al Qaeda branch.
The last major U.S. military contingent in Yemen had been stationed at the al-Annad air base in the south, according to national security sources.
State Department spokesman Jeff Rathke said all remaining US staff had been "temporarily relocated" but insisted that Washington would "continue to actively monitor terrorist threats emanating from Yemen and ... take action to disrupt continuing, imminent threats to the United States".
Washington for years has been waging a campaign of deadly drone strikes against al Qaeda operatives in Yemen. US officials say the unmanned aircraft fly out of a base in neighboring Saudi Arabia.
Only last September US President Barack Obama touted the partnership with Yemen as a model in counter-terrorism.
But the subsequent collapse of Hadi's government disrupted some U.S. counterterrorism operations, and the closing of the US embassy in Sanaa last month took a further toll.
Despite that, Hadi sounded a defiant note from his base in the south on Saturday, threatening action against the Houthis' northern stronghold.
"We shall deliver the country to safety and raise Yemen's flag on Mount Marran in Saadeh instead of the Iranian flag," he said in a televised speech, his first since reaching Aden. Iran is an ally of the Houthis, who belong to a Shi'ite Muslim sect.
The Houthis, in a statement from their Supreme Revolutionary Committee, did not directly respond to the speech but called for a "general mobilisation" of the armed forces against a "dirty war" they said was being waged by militias loyal to Hadi.
Hadi's flight to Aden has raised the prospect of armed confrontation between rival governments based in the north and south, creating chaos that could be exploited by the Yemen-based regional wing of al Qaeda.
Fighting is spreading across Yemen, and 137 people were killed on Friday in the bombings of two Shi'ite mosques in Sanaa. The bombings were claimed by Islamic State, an al Qaeda offshoot that controls large swaths of territory in Iraq and Syria and said it was also behind an attack that killed 23 people in Tunisia on Wednesday.
In his letter to Security Council, Hadi called for a resolution to "deter the Houthi militias and their allies, to stop their aggression against all governorates, especially the city of Aden, and to support the legitimate authority".
UN mediator Jamal Benomar is likely to brief the council on Sunday via video link, diplomats said. The Security Council is negotiating a statement on Yemen that could be adopted during the meeting, diplomats said.
"We join all of the other members of the Security Council in underscoring that President Hadi is the legitimate authority in Yemen," Rathke said in a statement released in Washington. He called on the Houthis and "their allies to stop their violent incitement" but made no mention of Iran, whose backing for the Houthis has raised U.S. concerns.
Hadi held open the door to a negotiated settlement with a call for the Houthis and other groups to attend peace talks in Saudi Arabia.
He said Yemen must return to the political situation in place before the Houthis took control of Sanaa, restoring its constitution and implementing the results of a national dialogue process and Gulf-sponsored political transition.
In his speech, he denounced the Houthis as "coup plotters" and said he wanted to confront sectarianism. Addressing Houthi accusations that he planned to back a southern secessionist movement, he said his flight to Aden had been intended to preserve the country's unity.
Unidentified warplanes have bombed Hadi's Aden headquarters in recent days, and on Saturday forces loyal to the former president, Ali Abdullah Saleh, who is now allied to the Houthis, moved units to Taiz, 150 km (100 miles) northwest of Aden.
On Friday, al Qaeda militants killed 20 soldiers during a brief occupation of al-Houta, the capital of Lahj province, which is only 30 km (20 miles) from Aden, before being driven back by the army.