The Saudi-led coalition in Yemen has vowed to respond “firmly and forcefully” to Houthi threats against vessels after the Iran-aligned group declared a maritime blockade on Saudi Arabia.

In a statement on Monday, the coalition said its Joint Forces Command had begun implementing measures to protect coalition vessels passing through the Bab al-Mandab Strait, a strategic gateway connecting the Red Sea with the Gulf of Aden.

The coalition condemned the Houthi declaration as a violation of international law and a threat to commercial navigation.

The Houthis said the blockade was retaliation for what they described as Saudi Arabia’s continuing siege of Yemen. It remains unclear how the group intends to enforce the measure or whether it will resume direct attacks against vessels linked to the kingdom.

Any disruption at Bab al-Mandab could have significant consequences for global trade and energy markets. The narrow waterway is one of the world’s most important maritime routes, connecting shipping between the Indian Ocean, the Red Sea and the Suez Canal.

The latest escalation comes after renewed Houthi missile and drone attacks against Saudi Arabia brought an end to a truce that had largely contained direct fighting between the two sides for four years.