The latest in a string of provocative Iranian maritime actions occurred on Monday when the destroyer USS Mahan was obliged to alter course, fire warning flares, and man its own weapons due to the close approach of an Iranian Revolutionary Guards Corps attack boat.

U.S. officials told Fox News the Iranian craft approached to within 1,100 yards from the Mahan at a “high rate of speed” and manned its weaponsThe Navy ship was securely within international waters in the Arabian Gulf at the time.

CNN quotes an American official describing the Iranians’ conduct as “unprofessional but also provocative.”

Unlike a previous incident, the Mahan did not fire any warning shots. ABC News mentions that the Navy ship fired its warning flare “in the direction” of the IRGC ship, but that doesn’t quite count as a warning shot.

In January, four Iranian vessels approached the U.S. destroyer after ignoring its radio calls to stay clear and fired three warning shots at them with a .50 caliber machine gun.

“According to the U.S. military, Iran harassed U.S. Navy warships through “unprofessional” interactions at least 35 times in 2016, a jump of more than 50 percent from the previous year,” Fox News reports.

One likely reason for the Navy’s apprehension about these aggressive Iranian approaches is that Iran claims to have deployed a new anti-ship missile, which can supposedly be launched from small boats. Few other claims about the capabilities of the new Nasir missile have been published by Iranian state media, but Defense Minister General Hossein Dehghan said the weapon system opens a “new chapter” in Iran’s missile technology.

“Equipping the Iranian naval forces with this missile marks an effective step toward increasing the country’s defensive capability and deterrence power,” Dehghan said in a report broadcast on Iran’s PressTV on Saturday.