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Saudi Arabia's Foreign Minister Adel al-Jubeir accused Yemen's Houthi rebels of stepping up their attacks on Thursday and of putting in danger a day-old UN-brokered ceasefire.

Jubeir told reporters in Washington that Saudi Arabia reserves the right to defend itself from further Houthi attacks, but stopped short of declaring the truce a failure.

"As of this morning Washington time there had been more than 150 violations by the Houthi-Saleh side," Jubeir said, referring to the rebels and forces loyal to former president Ali Abdullah Saleh.

A UN-brokered 72-hour ceasefire in Yemen came into effect on Wednesday night, after a day of heavy fighting and air raids, raising hopes of a more permanent truce.

Sitting with US Secretary of State John Kerry after talks at the State Department, Jubeir called the alleged Houthi attacks an "escalation in the violence, rather than a reduction."

And he accused the Houthis of launching a missile across the border into Saudi territory and killing a man and his daughter.

Kerry condemned the cross-border attack, but was keen to insist that his guest confirm that the Saudi-led coalition fighting in Yemen still intends to respect the ceasefire.

"If I can just interrupt," Kerry interjected as Jubeir finished his remarks.

"It is clear that Saudi Arabia is still committed to the ceasefire and as far as you're concerned the ceasefire is still in effect. Is that correct?"

Jubeir responded that the kingdom has indicated that it supports Yemeni President Abedrabbo Mansour Hadi's call for a truce.

"The coalition countries are abiding by this," he said.

"But I want to emphasise that we have a right to defend ourselves, we have a right to protect our borders, we have a right to protect our citizens and we have to ensure that the other side maintains its commitment to the cessation of hostilities."

On Thursday, reports emerged that Iran has increased its transfer of weapons to the Houthi rebels, a development that could prolong the country’s now 19-month-long war.

Agencies contributed to this report.