Yemen’s security forces closed the port al-Mukalla in Hadramawt on Wednesday after detecting drones believed to belong to the Iran-backed Houthi militia, local media reported citing sources.

The port was closed after hearing drones which security forces heavily fired at in an attempt to down them, Yemen Monitor reported, adding that it was not clear how many drones there were.

Last week, Yemen’s government said that its forces intercepted armed drones launched against al-Dhabba oil terminal, located in the town of al-Shihr in Hadramawt, as an oil tanker was preparing to dock.

The Houthis said they carried out a warning attack to prevent the vessel in al-Dhabba from “smuggling” crude oil from the port.

The incident at al-Dhabba was the first major escalation since the Houthis and the internationally-recognized government failed to renew a UN-brokered truce earlier this month, amid differences over payment of salaries for civil servants in Houthi-controlled areas.