After a three-day truce in Yemen's war expired, violence intensified as Iran-backed Houthis rebels and government supporters have continued to engage in fierce combat. In response to rebel attacks on the Saudi Arabia's territory, a Saudi-led coalition launched a series of airstrikes around the Yemeni capital Sanaa on Sunday.

They said the pre-dawn airstrikes targeted military facilities belonging to the Shiite Houthi rebels fighting the internationally recognized government. They had no word on casualties or damage.

Peace talks have so far failed. The ceasefire, agreed in order to allow an increased flow of humanitarian aid, ended without renewal after a day of heavy fighting between the Saudi-led Arab alliance and the Iran-allied Houthis. Each side accused the other of repeatedly violating the truce and U.N. attempts to extend it before it lapsed appeared to have failed.

"The [Houthis] coup militias deliberately thwarted the truce and that further convinced our military and political leadership of their unwillingness to accept a peace," the government's army chief of staff Mohammed Ali al-Miqdashi said on Saturday.

The last ceasefire attempt began in April and later collapsed alongside UN-brokered peace talks in Kuwait. The truce was the sixth attempt since the Saudi-led coalition intervened in March last year to support the government of President Abedrabbo Mansour Hadi. The United Nations and diplomats had hoped a pause in the conflict would pave the way for talks to end a 19-month-old war which has killed at least 10,000 people in the Arabian Peninsula's poorest country.

Ismail Ould Cheikh Ahmed, the UN's Yemen envoy called on all parties to the conflict to continue the truce for at least another 72 hours, saying that it was largely holding "despite reported violations from both sides in several areas."

Tension has escalated in the war-torn country after the Saudi-led campaign in Yemen has come under heavy criticism since an airstrike this month on a funeral gathering in the Yemeni capital Sanaa that killed 140 people, according to a United Nations' estimate, 82 according to the Houthis. In another major development, the US Navy for the first time targeted Houthis directly. On Oct. 13, it hit radar sites which, the US said, were involved in missile launches against a US warship and other vessels.

The war in Yemen began in 2014 when Shiite rebels, known as Iran-backed Houthis based in the north, seized the capital Sanaa. In March 2015, Saudi Arabia and its Gulf allies launched a campaign of airstrikes against the rebels. The Saudi-led coalition and the U.S. are backing the internationally recognized government of President Hadi.