SANAA (Reuters) - Yemen's dominant Houthi movement launched Katyusha rockets into Saudi Arabia on Sunday and residents reported Saudi-led air strikes in a Yemeni border province in exchanges that threatened to derail a 48-hour truce.

The Houthis said the rocket salvo targeting a military base in the kingdom's southern Najran province was launched in response to Saudi shelling on Yemeni border villages.

There was no immediate response from the coalition to the Houthi assertion.

The coalition, which has been fighting the Iran-aligned Houthis to restore ousted Yemeni President Abd-Rabbu Mansour Hadi to power, announced the truce on Friday night as a step to end a 20-month old war that has killed more than 10,000 people and displaced more than three million.

Just three days earlier, Hadi's government had rejected an announcement by U.S. Secretary of State John Kerry that the warring parties had agreed to an open-ended truce and to work toward the formation of a unity government.

Hadi's government complained it was not consulted about the accord unveiled by Kerry on Nov. 15 after a visit to Oman and the United Arab Emirates. It said the accord did not account for demands for the Houthis to withdraw from cities they had captured since 2014.

The Houthis in turn have cast doubt on the 48-hour truce announced by the Saudi-led coalition, saying it was designed to undermine the agreement reached in Oman last week.

The Houthi-run Saba news agency said that at a meeting in Sanaa, the ruling supreme political council comprising the Houthis and former President Ali Abdullah Saleh's General People's Congress party "welcomed all efforts to end the aggression, foremost of which (are) the efforts of the Sultanate of Oman to achieve peace in Yemen".

The U.N. envoy to Yemen, Ismail Ould Cheikh Ahmed, said the parties have agreed to resume meetings of a "De-escalation & Coordination Committee" by deploying representatives to southern Saudi Arabia.

"I remind all parties that terms and conditions of cessation of hostilities include a full and comprehensive halt to military activities," Ould Cheikh Ahmed wrote.

Separately, residents in the far northern Yemeni province of Hajja reported Saudi-led air strikes in the Hiran district.

A spokesman for the Saudi-led coalition did not immediately respond to a Reuters request for comment. But General Ahmed al-Asseri told U.S. news network CNN's Arabic service that the Houthi violations were too frequent to be counted, and suggested that the truce would not be renewed.

"The Arab coalition has heeded a request by the Yemeni government and the international community and declared a truce, but any truce without monitoring on the ground is useless because we are facing an armed militia," he said according to CNN.

The coalition of mostly Gulf Arab states intervened in Yemen's civil war in March 2015 to restore Hadi to power. It has launched thousands of air strikes against his foes in the Iran-allied Houthi movement but has yet to dislodge the group from the capital Sanaa.

(Reporting By Mohammed Ghobari; Writing by Noah Browning; Editing by Sami Aboudi and Tom Heneghan)