Iranian naval forces intercepted six ships in the Strait of Hormuz on Sunday after the ships tried to transit through routes Iran has not approved.
Warning shots were fired. The ships were ordered back.
State television said one was involved in an "incident" and gave no further details.
A day earlier, on Saturday, the Guards stopped four other ships attempting the same transit in the same water. Warning shots were used in that operation too.
Iran has operated a blockade in the strait since the outbreak of the US-Iran conflict earlier this year. The Revolutionary Guards Navy has enforced designated transit corridors and turned back ships that deviate from them.
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