Yemen's Houthi rebels have accused the Saudi-led coalition of bombing the country's main international airport, destroying a navigation station that is critical to receiving already limited aid shipments.

Houthi officials told Al Jazeera two air strikes targeted Sanaa's international airport in the rebel-held capital early on Tuesday, making it unusable for aid flights and further complicating humanitarian efforts into the country.

"This attack is intended to cause maximum damage and deprive millions of Yemenis from receiving life-saving food and medicines," Mohammed, a Houthi official who declined to give his surname, said.

The Saudi-led coalition forced the closure of Sanaa airport in August 2016 to all but a few UN aid flights.

The Houthi-run General Authority for Civil Aviation said in a statement the air strike "led to the total destruction of the VOR/DME radio navigation system, taking it offline and thus halting the only flights at Sanaa airport - those of the UN and other international organisations delivering humanitarian assistance".

"The authority emphasises that attack is an explicit violation of international covenants and treaties, which stipulate that civilian airports are not targeted," it added.

Last week, the Saudi-led coalition intensified its embargo on Yemen, closing all of the country's land, sea and air ports after Houthi rebels fired a ballistic missile towards the Saudi capital, Riyadh.

The kingdom intercepted the missile and no one was injured, but within hours it imposed a fresh blockade, claiming it aimed at preventing weapons being smuggled into Yemen by its regional rival, Iran.

We heard [from the Saudis] that Aden and Mukalla ports are now open - but this is not enough. This does not replace Hodeidah port and Sanaa airport - we need to allow these ports to operate as normal. Humanitarian aid cannot replace commercial shipments. Rasha Muhrez, Save the Children

On Monday, the coalition said it would ease the blockade and allow flights to Aden and open the southern city's port, but it refused to reopen Hodeidah port.

The UN says the closure of Hodeida port puts millions of civilians in the north at risk. Aden port, which is controlled by the coalition, does not have the capacity to handle the volume of humanitarian cargo and would mean hazardous cross-line deliveries.

'Immediate assistance'

George Khoury, the UN country director for Yemen, told Al Jazeera he was "concerned" Tuesday's air strikes could affect operations in the country.

"Millions of Yemenis depend on this airport for aid and we have hundreds of staff use it to move in and out of the country," he said.

"We are still assessing the situation ... but are extremely concerned at the risk posed to our supply pipelines."

Yemen used to import about 70 percent of its daily needs before the blockade, but since the start of the siege, food and medicine are in short supply, with cooking gas prices having surged by around 100 percent and fuel unavailable at most gas stations.

"Seventy percent of families in Yemen live from hand to mouth, they buy from the shops and eat that very night at the table. If there is any breach in our supply pipeline, it will greatly impact millions," Khoury added.

Speaking to Al Jazeera from Sanaa, Rasha Muhrez, director of operations at the charity Save the Children, said aid agencies were struggling to contain the crisis.

"If we don't have the fuel to deliver our supplies to millions of starving Yemeni families, we will continue to witness more children dying of hunger," Muhrez said.

"We heard [from the Saudis] that Aden and Mukalla ports are now open - but this is not enough. This does not replace Hodeidah port and Sanaa airport - we need to allow these ports to operate as normal."

Muhrez said, more importantly, humanitarian aid cannot replace commercial shipments. "There are about 27 million people in need, over seven million of whom are facing famine-like conditions. They need immediate assistance."

Yemen has been devastated by war since 2015 when Houthi rebels captured Sanaa and overthrew President Abd-Rabbu Mansour Hadi's government.

Together with a coalition of other Arab states, and with logistical support from the United States and other western powers, Saudi Arabia intervened - but has so far failed to dislodge the rebels from Sanaa and their northern strongholds.

The civilian death toll has surpassed 10,000 and millions have been brought to the brink of starvation.

Follow Al Jazeera's Faisal Edroos on Twitter: @FaisalEdroos