SANAA, Yemen — Loyalists of former Yemeni leader Ali Abdullah Saleh seized the country's main airport Saturday as tanks and armored vehicles occupied the tarmac and forced authorities to cancel flights, a day after a military shake-up in which key commanders were fired.

Driving pickup trucks mounted with anti-aircraft guns, armed tribesmen along with troops in uniform blasted buildings of Sanaa International Airport and opened fire on one of the airport surveillance towers before surrounding the entire complex, blocking roads and turning away passenger vehicles.

The standoff highlighted the challenges facing the country's new leader, who must balance a promise to purge ex-regime elements from the army with the lingering influence of his predecessor.

At stake is the stability of the Arab world's poorest country where al-Qaida is poised to fill the vacuum.

Yemen's new president, Abed Rabbo Mansour Hadi, fired several generals and other figures from the old regime Friday in a bid to show he was making good on promises of reforms and to appease protesters worried Saleh is trying to wield power from behind the scenes.