DUBAI, United Arab Emirates (AP) — A multinational coalition of navies says it will step up patrols in waters around Yemen after several attacks there, including those launched by Somali pirates and others blamed on Yemeni rebel forces.

The Bahrain-based Combined Maritime Forces issued a statement to shippers Monday outlining the threats in the Gulf of Aden and Bab el-Mandeb, two crucial areas for shippers transiting the Suez Canal.

The maritime force noted one attack in May saw one of the boats attacking a vessel explode “for an unknown reason.”

Lt. Ian McConnaughey, a spokesman for the U.S. Navy’s 5th Fleet in Bahrain, declined to elaborate on who authorities believed was behind that attack.

McConnaughey tells The Associated Press: “We want people to focus on all of the threats and not think about one or the other.”