Iran's coast guard has seized a towboat and detained its 12 crew members from the Philippines near the Strait of Hormuz.
The boat was carrying nearly 284,000 liters of diesel, the news agency ISNA said on Saturday.
Iran has frequently seized boats it says are being used for smuggling oil in the Gulf.
Earlier on Wednesday Iran allowed seven foreign crew members of the British-flagged Stena Impero oil tanker to leave the country.
In July, Iran seized the tanker after Britain seized an Iranian tanker in Gibraltar, which was released later.