The Houthis announced firing three ballistic missiles at Saudi military positions on Sunday evening.

Houthis fired the Iranian-made Zelzal-1 missiles at gatherings of "mercenaries of the Saudi army," according to Houthi-run Al-Masirah TV channel, which left dead and wounded.

It was the first missile attack by Houthi forces on Saudi Arabia since Qods Force Commander Qassem Soleimani was killed Friday in a U.S. airstrike targeting him and a pro-Tehran Iraqi commander Abu Mahdi Al-Muhandis at Baghdad airport. The Houthis ended a months-long ceasefire on missile attacks in late December in response to a Saudi airstrike the rebels say targeted a market in Yemen's Sa'ada governorate. 

Earlier, Hassan Nasrallah, secretary general of Lebanon's Hezbollah, vowed that all those who described themselves as "resistance forces" would respond to the incident. "Qassem Soleimani is not a purely Iranian affair," he said, but one that concerns "all axis of resistance," referring to the alliance of pro-Iranian militias including Lebanon's Hezbollah, Shiite factions and parties in Iraq and Yemen, and the Syrian regime.

On Friday, the Houthis said that the crime would not go without a response, pointing to the solidarity of the rebels group with Iran and its resistance to the Americans.

Saudi Arabia was quick to offer appeasement over the killing of Soleimani. "In view of the rapid developments, the Kingdom emphasizes the importance of demonstrating restraint to prevent any action that could lead to an escalation," a Saudi official who asked not to be identified told AFP.

The Saudi Foreign Ministry on Friday called for restraint, while King Salman bin Abdul Aziz called for urgent measures to "reduce tensions" in a telephone conversation with Iraqi President Barham Saleh, the Saudi Press Agency reported.

In another telephone conversation with the Head of the Iraqi Caretaker Government Adel Abdul Mahdi, Saudi Crown Prince Mohammed bin Salman stressed the need to calm the situation, the Saudi news agency said.

The Saudi newspaper "Middle East" reported that the crown prince instructed his younger brother, Deputy Defense Minister Prince Khalid bin Salman, to go to Washington and London in coming days to convey this call for restraint. Prince Khalid will meet with senior officials at the White House and the Departments of State and Defense in Washington, the newspaper said.

Saudi Arabia is leading a coalition of Arab states to support the Yemeni government against the Iran-aligned Houthis, and the kingdom says it is seeking to defeat the Iranian project in Yemen rather than root out the Houthis.

Since the devastating attack on Saudi oil facilities in mid-September, the kingdom and the Houthis have sought to calm tensions by agreeing to a ceasefire on cross border attacks. Yemen has since witnessed a relative lull in fighting between the two sides amid reports of indirect consultations between the kingdom and the Houthis. The release of prisoners from both sides during this period seems to indicate progress in the negotiations.