DUBAI, United Arab Emirates—The U.S. Navy announced Sunday it seized a boat in the Gulf of Oman carrying fertilizer used to make explosives that was caught last year smuggling weapons to Yemen. The British royal navy said it confiscated 1,041 kilograms (2,295 pounds) of illegal drugs in the same waters. The interdictions were just the latest in the volatile waters of the Persian Gulf as American and British authorities step up seizures of contraband during the grinding conflict in Yemen and ongoing drug trafficking in the region. The U.S. Navy’s Mideast-based 5th Fleet said its guided-missile destroyer USS Cole and patrol ships halted and searched the sailboat, a stateless fishing dhow, that was sailing from Iran on a well-worn maritime arms smuggling route to war-ravaged Yemen last Tuesday. U.S. forces found 40 tons of urea fertilizer, known to be a key ingredient in homemade improvised explosive devices, hidden on board. …