RIYADH－The Saudi-led military coalition launched airstrikes on Yemen's capital on Monday, the coalition and Yemeni security officials said, just two days after a foiled drone and missile attack targeting Saudi capital Riyadh.

The Saudi-led strikes appeared to signal an escalation in the coalition's bombing campaign in Yemen.

The coalition has been fighting Yemen's Houthi rebels since March 2015.

Coalition officials said in a brief statement that they had started an operation to "destroy legitimate military targets" held by the rebels. It did not elaborate.

The officials said more than 12 airstrikes hit rebel-held Sanaa on Monday, including six on a military academy north of the capital and four on a military air base that is within the Sanaa International Airport. Further airstrikes were reported in the northwestern Amran Province.

There were no immediate reports of injuries, but residents said ambulances rushed to areas where the airstrikes took place.

Saudi Arabia's Air Defense Forces on Saturday intercepted and destroyed a ballistic missile over the capital Riyadh around midnight. Another missile was also intercepted and destroyed over the southern Saudi city of Jizan, which borders Yemen.

The Houthis frequently launch missiles across Yemen's border into Saudi Arabia, but they rarely reach the capital. Riyadh is around 1,000 kilometers north of the border with Yemen.

Elsewhere in Yemen, officials said fierce clashes between Yemeni government forces and the rebels in the mountainous northern province of Jawf and neighboring Marib killed more than 45 from both sides in the past two days.

The officials said the Houthis attempted to seize control of the Sirwah district, but government forces repelled the Houthi attack.

The UN Special Envoy for Yemen, Martin Griffiths, on Sunday voiced concerns about the escalation of fighting in Marib and rebel attacks on Saudi Arabia.

"I am gravely dismayed and disappointed by these actions at a time when the Yemeni public's demands for peace are unanimous and louder than ever before," he said.

He called for the focus to be on "averting and mitigating the potentially disastrous consequences" of the COVID-19 pandemic.

The recent escalation of fighting in Yemen has displaced more than 40,000 people since January, adding to the roughly 3.6 million who have fled their homes since the war began five years ago.

A number of those fleeing in recent weeks, including women and children, escaped on foot, walking for days without food or water across open desert, according to a recent statement by the United Nations Refugee Agency.

Yemen's civil war erupted in 2014. Over the years, the war has killed more than 100,000 people, many by Saudi-led airstrikes. It has led to millions suffering from food and medical shortages.

Xinhua - Agencies