"Yesterday, the coast guards deployed in the country's southern waters came to spot two vessels in Iran's protected waters in the south using electronic and optic tools and equipment," the Fars News Agency quoted Qalandar Lashkari, commander of Bushehr province's coast guard, as saying.
Lashkari said nine sailors were arrested, adding they were nationals of different countries.
Islamic Revolutionary Guards Corps forces earlier this year seized another Saudi vessel that illegally entered Iran's territory, later expelling the craft and its four-person crew.
In January, Saudi Arabia detained 21 Iranian nationals on two boats that were about 40 miles off the Saudi coast, Fars said.
Ray Liotta sues skin care company over use of likeness
Kim Kardashian, Kanye West reportedly set wedding date