The threat from Yemen's Houthis, who announced a naval blockade of Saudi Arabia, could escalate into an "even broader" regional conflict, a spokesperson for the UN secretary-general warned.

"We have seen these reports and are deeply concerned about the renewed threats by the Houthis against Saudi Arabia and freedom of navigation, which carry the risk of even greater regional escalation," UN Secretary-General spokesperson Stéphane Dujarric told reporters.