The Yemeni coastguard detained on Tuesday vessels from Russia and Mongolia in Yemeni territorial waters in the Red Sea, the Elaph online portal said, quoting a coastguard spokesman.
Fishermen had reported that two "suspicious" vessels had entered Yemeni territorial waters, spokesman Abdullah Mohammed Jalil told journalists.
A total of 27 crew members belonging to "various European nations," were on board the ships, he said, adding that "19 weapons of various kinds" were found on board the Russian vessel.
Both vessels were reported to have been convoyed to a port in the western Hodeidah province.
A spokesman for the Russian embassy in Yemen told RIA Novosti the report was being investigated.
"There have been no official reports from the Yemeni side... about the detention of Russian citizens, as well as those from the Commonwealth of Independent States (CIS) countries," he said.
"It is unlikely that those [detained] may be Russian or CIS nationals," he said. "We don't have any information confirming this."