Iran has seized three vessels belonging to one of the Arab states of the Persian Gulf after they entered Iranian territorial waters.

According to Fars news agency, the vessels were seized while in Iran’s territorial waters by 12 kilometers.

“Twenty-one crew members were also arrested,” it added.

This is not the first time foreign naval forces have entered Iran’s water.

On January 12, 2016, two U.S. Navy riverine command boats were seized by Iran's Islamic Revolutionary Guard Corps (IRGC) Navy after they entered Iranian territorial waters in the Persian Gulf.

The U.S. military initially claimed that the sailors have entered Iranian waters due to technical failure, but it was later reported that the incident happened because of navigational errors.

Following an exchange of phone calls between U.S. Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif, the sailors were released, unharmed, 15 hours later.

Kerry later thanked Iranian authorities for their cooperation, adding that “we can all imagine how a similar situation might have played out three or four years ago.”

Obama administration hailed the release as an “unintended benefit” of the new diplomatic relationship with Iran established by the nuclear accord, while some of his Republican rivals, including presidential hopefuls such as Ted Cruz and Donald Trump criticized the U.S. response as being “too weak”.