The airport in the Yemeni capital, Sanaa, has been shut down after forces loyal to a military ally of former president Ali Abdullah Saleh threatened to attack landing and departing aircraft, according to an airport source.
The source said Saturday's closure came after the airport was surrounded by loyalists of the air force chief, General Mohammed Saleh al-Ahmar, a half-brother of Saleh, who has refused to step down after being sacked by Abd-Rabbu Mansour Hadi, the current president.
"No aircraft has taken off or landed since these forces made their threat late on Friday," the source said, adding that the troops surrounding the airport were backed by members of the Hamdan tribe that supports Saleh.
The source, speaking on condition of anonymity, said the men were led by Naji Jamaan, a Hamdan tribal chief.
Speaking to Al Jazeera by phone from Sanaa, Mohammed al-Qadhi, a Yemeni journalist, described the situation in the city as "very tense", with Saleh loyalists on standby in the southern areas.
Mohammed Saleh al-Ahmar has refused to step aside unless several senior defence ministry officials also leave, a military source said on Saturday.
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In a message to his troops, the dismissed head of the air force said Hadi's presidential decree would not be "implemented" until Mohammed Nasser Ahmed, the defence minister, General Ali Mohsen al-Ahmar and Ali al-Ashwal, the chief of staff, left their posts.
The move against Mohammed Saleh al-Ahmar comes amid almost daily protests demanding the resignations of all Saleh relatives from the government and the military.
"For more than two months now, there have been strikes and protests" demanding Ahmar's removal", Qadhi told Al Jazeera on Saturday.
Hakim al-Masmari, editor in chief of the Yemen Post, told Al Jazeera that Hadi has "no other choice" but to make the dismissals.
"He became president under one condition: he would be able to start a national dialogue a week after he takes power," Masmari said.
"It's been a month and a half and the opposition factions have refused to enter any dialogue with President Hadi unless military reforms take place immediately."
In addition to the air force chief, Hadi dismissed on Saturday the head of the presidential guard, General Tareq Mohammed Abdullah Saleh, a nephew of former president Saleh.
The military source said Tareq had also refused to quit and had turned down an offer to command of the 37th Battalion of the Republican Guard in the southeastern province of Hadramawt.
Still in command
Gulf Co-operation Council chief Abdullatif al-Zayani, who led mediation efforts to convince Saleh to step down, said the six-nation group "supports" Hadi and "backs all measures he takes to help Yemen exit its current crisis".
Zayani also "urged all political power players in Yemen and all those involved to support the Yemeni president to move forward in implementing the principles stipulated by the Gulf initiative".
That initiative, under which Saleh resigned after 33 years in power in exchange for immunity from prosecution, includes a restructuring of the army as one of several conditions.
During his years in power, Saleh chose his aides carefully and many remain in control of security bodies. Critics say he has been interfering in the transition of power.
Saleh's son Ahmed still heads the elite Republican Guard, while a nephew, Yehya, commands central security services.
In a February speech, Hadi stressed the need to reunify the army as he pledged "radical reforms" and to fight al-Qaeda as he outlined a two-year transition plan.