It has been a week since Yemen's Iran-backed Houthi rebels entered down the Red Sea coast, extending their reach to a maritime choke point, and threatened Saudi Arabia's oil exports.
The Houthis' biggest acquisition in years reignited Yemen's 12-year civil war and has already pushed up global fuel prices.
The Houthis are firing at Saudi oil facilities and tankers. Their attack on Saudi Arabia's east-west pipeline, blamed on Iran-backed militias in Iraq, added to an unfolding situation for the kingdom and rattled world markets.
The Houthis captured the Red Sea port city of Mokha before taking several islands near the narrow Bab el-Mandeb strait through which some 12 per cent of world trade passes in peacetime.
The Houthis first swept down from their northern heartland in 2014, capturing the capital, Sanaa, and much of northern Yemen.
The capturing of Mokha and the islands in the Bab el-Mandeb strait allows the Houthis to "harass shipping more easily", said April Longley Alley from the Washington Institute.
The Houthis perceive Saudi Arabia as "more vulnerable" due to the Iran war, she said.
Windward, a shipping firm, reported a dip in traffic through the Bab el-Mandeb strait from 35 daily transits before the Houthi advance to 25 after, but traffic has already recovered and climbed to 45 transits on Sunday.
The health ministry of the Saudi-backed government says the Houthis have killed around 150 civilians since September 3.
Saudi Arabia said Thursday that debris from an intercepted Houthi drone killed one person and wounded two others in the kingdom.