At least 31 Houthi rebels were killed Friday in airstrikes launched by the Saudi-led coalition in Yemen's central province of Marib, a military source from the Yemeni government told Xinhua.

"The airstrikes killed the militants in the desert while they were moving in three groups toward positions of the Yemeni army in the western district of Sirwah," the source said on condition of anonymity.

Meanwhile, Houthi-run al-Masirah TV reported 15 coalition airstrikes on the Houthi positions in Sirwah, without providing further details.

The Iran-backed Houthis began in February a major offensive against the Saudi-backed Yemeni government army to capture the oil-rich province of Marib, which hosts nearly 2 million internally displaced people.

The United Nations has warned the offensive on Marib could lead to a major humanitarian catastrophe.

A recent UN-brokered negotiation between Yemen's warring sides and other relevant parties has failed to produce a cease-fire agreement.

Yemen has been mired in a civil war since late 2014 when the Houthi militia seized control of several northern provinces and forced the internationally recognized government of President Abd-Rabbu Mansour Hadi out of the capital Sanaa.

The Saudi-led Arab coalition intervened in the Yemeni conflict in March 2015 to support Hadi's government.