facebook.com/Andrii Klymenko
The vessels were intercepted off Ukraine coast near Berdyansk and Mariupol.
Coast guards of Russia's Federal Security Service (FSB) over the past day detained in the Sea of Azov seven merchant ships heading to or from the Ukrainian sea ports of Mariupol and Berdyansk.
Read alsoRussia's coast guards detain seven ships off Ukraine coast in Sea of Azov since Monday evening
"From 00:30 to 23:00 on July 8, Russia's FSB coast guard motor boats intercepted six vessels going from/to Berdyansk or Mariupol [the area is marked on the map in yellow]," Andriy Klymenko, head of the supervisory board at the Maidan of Foreign Affairs Foundation and editor-in-chief of the portal BlackSeaNews, wrote on Facebook.
Russian FSB cost guards set a new "record" while the earlier top number of ships detained in one day accounted to five on July 4.
According to Klymenko, another vessel was intercepted in the same area around 01:00 overnight Monday, July 9.
Ukrainian intelligence earlier reported that Russia had deployed about 40 warships in the Sea of Azov.