DOHA, July 21. /TASS/. Six merchant ships have changed course over the past day after warning the Houthis from the Ansar Allah rebel movement about the imposition of a naval blockade of Saudi Arabia, Yemeni SABA news agency controlled by the rebels said.

"Over the past 24 hours, six vessels turned back after a warning by the Yemeni armed forces (controlled by the Houthis - TASS) and a ban on maritime shipping for [Saudi Arabia] as part of a 'blockade for blockade' formula," the agency quoted a military source as saying.

Earlier, Reuters reported that international shipping companies receive messages from the Houthi in Sanaa demanding that they refrain from loading and unloading in the Saudi ports. According to the agency, the rebels warned the carriers that cooperate with the kingdom's ports would make their vessels legitimate targets and expose them to attacks "in the area of operations conducted by the Yemeni armed forces."

On July 20, the Houthis imposed a naval blockade of Saudi Arabia, accusing the kingdom of years of "plundering Yemen's national wealth," which refers to its oil resources. On July 21, the Saudi-led Arab coalition announced measures to protect merchant ships in the Bab-el-Mandeb Strait. The alliance's official representative Turki al-Maliki said that any threats to navigation would be met with "resolute and harsh measures," describing the rebels' actions as maritime piracy.