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. 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. 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.