Amid the ongoing Saudi-led airstrikes in Yemen against the Houthi rebels, Iran is reportedly mulling to supply the Shi'ite militia group with surface-to-air missiles.

The Wall Street Journal cited a senior American defence official as saying that Washington is aware of the Shi'ite-inclined Iran's attempt to deliver the game-changing weapons to Houthis.

Iran has been accused of providing weapons and training to Houthi rebels, who are being pounded by the Saudi-led Sunni alliance forces, but both Houthis and Iran have denied the allegations.

"We are looking. We know they are trying to do it," a defence official was quoted as saying. If the Houthis lay their hands on surface-to-air missiles, they would be able to put up a major challenge against Saudi Arabia's military campaign. The supply of these weapons remain a cause of concern for the US and Saudi Arabia.

The continuing unrest in Yemen is widely seen as a proxy war between Shi'ite-inclined Iran, which has been accused of orchestrating the Houthi rebel militia in Yemen, and the Sunni powerhouse of Saudi Arabia.

The Saudi-led operation has received stinging criticism from its regional rival and heavyweight Iran repeatedly. However, Riyadh is determined to carry out their military campaign against the Houthis, who were on an offensive capturing several territories in Yemen.

Houthis have been struggling to receive weapons via air and naval routes, as multiple nations are keeping a close watch on the possible blockade of the potential channels. The US has also said they are stepping up intelligence cooperation with Saudi Arabia in their support for the armed intervention in Yemen.

As part of widening US operations in Yemen, American warships are searching Yemen-bound vessels in the region to halt potential arms delivery.