A man picks his way through the debris of a destroyed building in Sanaa, Yemen, on Nov. 1, 2018. The building allegedly had been hit in a Saudi-led airstrike. (Yahya Arhab/EPA-EFE/Shutterstock)

Clashes erupted in a strategic Yemeni port city and airstrikes pummeled the country’s capital on Friday, as the U.S.-backed Saudi-led coalition launched a fresh offensive in the Middle East’s poorest country, two days after an American call for a cease-fire.

A spokesman for the coalition said its forces attacked the international airport in the capital, Sanaa, and a nearby air base operated by Houthi rebels. The rebels were using the air base to launch attacks on the kingdom with drones and missiles, the spokesman, Col. Turki al-Maliki, told al-Ekhbariya TV, a Saudi state-owned broadcaster.

The Houthis, through their own television station, confirmed that more than 30 airstrikes had targeted the air base and other areas around the capital.

Meanwhile, the Saudi-led coalition appeared to have launched a fresh offensive against the Houthi-controlled port of Hodeida, according to Yemeni government sources and local media. Fighting was reported early Friday in southern and eastern areas of the city.

The port is a vital gateway for the imports of food, medicines and other essential supplies, as well as much of the humanitarian aid heading to northern Yemen. The assault followed reports this week of the coalition’s sending more than 10,000 reinforcements toward Hodeida via a southwestern coastal route.

“Fierce battles between forces backed by Saudi-led coalition and the #Houthis have been going on for hours in the southern and eastern outlets of the Red Sea port city of #Hodiedah, with huge blasts being heard and airstrikes,” Yemeni journalist Mohammed al-Qadhi wrote in a tweet Friday morning.

Friday’s assault comes two days after the United States called for a cease-fire and negotiations within 30 days to end the war. The fresh offensive could be designed to pressure the Houthis to come to the negotiating table, which the rebels have so far avoided.

Saudi Arabia and the United Arab Emirates are part of a regional coalition that is seeking to oust the Houthis and restore Yemen’s internationally recognized government. But the Houthis, who control the capital and much of northern Yemen, have so far showed few signs of weakening in the three-year-long conflict that has become a military stalemate.

The Saudi-led coalition of Sunni Muslim nations is also wary of the spreading influence in the region of Iran’s Shiite theocracy, widely said to be backing the Houthis. The United States, meanwhile, is supporting the coalition by refueling its jets, providing intelligence and selling its members arms worth billions of dollars.

Trapped between the warring parties are millions of Yemenis grappling with what the United Nations describes as the world’s most severe humanitarian crisis. This month, the United Nations declared that as many as 14 million Yemenis — nearly half the population — are on the brink of famine. More than 3 million have fled their homes, and a cholera epidemic is raging.