New Delhi, July 30 -- Yemen's Houthi rebels said they will target merchant ships belonging to any company that does business with Israeli ports, regardless of nationality, as part of what they say is a new phase of their operations against Israel.

The Iran-backed Houthis launched a campaign targeting ships in response to the Israel-Hamas war in the Gaza Strip, saying they were doing so in solidarity with the Palestinians. Their attacks over the past two years have upended shipping in the Red Sea, through which about $1 trillion of goods passes each year.

In an announcement late Sunday night, the Houthis said they had "decided to escalate their military support operations and begin implementing the fourth phase of the naval blockade" aga...