A boat allegedly being used to smuggle the fertiliser into Myanmar was also seized.
Acting on a tip-off, a Coast Guard vessel conducted the operation around 2 am, Coast Guard Media Officer Lieutenant Commander Sabbir Alam Sujan said in the afternoon.
He said the Coast Guard signalled a suspicious boat to stop, but it ignored the instruction and attempted to flee.
The patrol team gave chase and intercepted the boat in the deep sea.
A search uncovered 10,000kg of urea fertiliser, valued at approximately Tk2.5 lakh, allegedly being transported illegally for smuggling into Myanmar.
The nine people on board were detained, and the boat was seized.
Sujan said legal proceedings concerning the detainees, seized fertiliser and boat were under way.
He added that Coast Guard operations against smuggling would continue.
