British Maritime Security firm Ambrey said a Marshall Islands-flagged, US-owned bulk carrier was reportedly struck by a missile while transiting near Yemen’s port of Aden, AFP reports.

The vessel was assessed not to be Israel-affiliated, according to Ambrey, which also assessed the attack to have targeted US interests in response to the recent strikes on Houthi military positions. The latest attack suggests that despite the US strikes, the Houthis appear undeterred.

Later on Monday, an explosion was heard near Yemen’s Hodeidah airport, residents reported. Hodeidah is some distance from Aden, however, and it was not immediately clear what had caused the blast.

Many ships have been forced to take the longer route via the Cape of Good Hope instead. Ship-tracking data on Monday showed at least 15 tankers altering course in response to the escalating conflict.