Feb. 18 (UPI) -- South Korea is in diplomatic discussions with Russia following the seizure of a South Korean fishing boat by Russian authorities.

Seoul's foreign ministry said Monday the boat was recently taken into Russian custody. Five out of the 11 crewmembers are South Korean nationals, News 1 reported Monday.

The 69-ton fishing vessel from Uljin, South Korea, was detained on Sunday at 6:30 a.m. Russian authorities say the boat was caught "fishing illegally," according to the report.

The boat's crew was taken to Nakhodka, a port city in the Russian Far East, where they await a final decision. On Monday morning, Russia informed the South Korean consulate in Vladivostok about the arrests.

South Korea says the crew was fishing for crabs when they were detained.

Seoul's diplomats based in Vladivostok are to interview the crew, make contact with Russian diplomats and border security officials to find out the details of the arrest, Tongil News reported.

Reporting of the incident comes at a time of deteriorating U.S.-Russia relations, but also as Seoul continues to cooperate with Moscow for dealing with Korean Peninsula security.

Anthony Rinna, an analyst on Russian foreign policy for the Sino-NK research group, said in an analysis published Monday South Korea has "adopted policies in the realm of missile defense that run counter to Russian interests," but mutual economic interests prevailed over a possible crisis over the deployment of THAAD in 2017.

South Korea's New Northern Policy, an "economic initiative" that could bring the economies of Russia and the two Koreas closer together, has also signaled rapprochement, Rinna writes.

Russia may be cooperating on sanctions, and has said it plans to repatriate all North Korean laborers by the end of 2019.

In November, Russian Ambassador to North Korea Alexander Matsegora had said a population of 34,000 North Korean workers in Russia had declined to about 11,000, as Russia complies with sanctions.