RIYHADH — Saudi Arabia's King Salman has ordered the National Guard, a ground force that exists apart from the army, to mobilize for operations against rebels in Yemen, the official SPA news agency said Tuesday.

It did not clarify how the National Guard would take part in the operation, which has seen a Saudi-led coalition launch air strikes against the rebels.

SPA quoted National Guard Minister Prince Miteb bin Abdullah as saying he was "honored" by Salman's "decision that National Guard forces take part" in the operation.

He signaled the "complete readiness of all National Guard forces to carry out this role alongside other military bodies" in Saudi Arabia.

The force is to "take part in defending the security" of the kingdom, SPA reported, without elaborating.

Saudi Arabia launched the air war against Iran-backed rebel forces in Yemen on March 26. It has so far rejected mounting a ground offensive but Saudi troops have clashed with the rebels in border areas.

The National Guard is a parallel army in Saudi Arabia separate from the armed forces run by the defense ministry.

Recruited from tribes that have traditionally backed Saud dynasty rule, it is a pillar of support for the royal family.

It is led by Miteb, the son of the late King Abdullah and educated at the elite Sandhurst military academy.

The guard is a trained army of 100,000 men, divided into infantry units, mechanized brigades, special units and military police.