Russia border authorities detained two North Korean vessels and dozens of crew members on Tuesday after several Russian guards were injured in gunfire during a maritime patrol. The Federal Security Service (FSB), the internal security services, said they have detained 161 fishermen after a Russian patrol was shot at. It had discovered two North Korean boats fishing illegally in Russian waters in the Sea of Japan, something that has been on the rise in recent months, straining relations between the two allies. Three Russian border guards were initially reported to have been injured during the incident and according to the Interfax<em> </em>news agency, the North Korean boats were taken to the far eastern port city of Nakhodka. By Wednesday, the number of guards injured had risen to four, according to the investigative committee probing the incident. "During the inspection of the vessel, North Korean poachers put up a fight against members of the inspection team. As a result, four employees have been injured to various degrees, one of them sustained a gunshot wound," a spokesperson said in comments carried by the TASS news agency. The Russian Foreign Ministry issued a statement on Tuesday saying the authorities were “taking decisive steps to detain the persons who attacked the members of the patrol group, injuring Russian border service personnel". “We have demanded that North Korea take comprehensive measures to avoid such incidents in the future,” it said, employing unusually forceful language. The Foreign Ministry also summoned a senior North Korean diplomat, Charge d’Affaires Jin Jong-hyeop, from its representative office in Moscow over the incident. Russia has been framed as a natural ally of the isolated North Korean regime. Moscow has routinely been accused of aiding Pyongyang evade United Nations sanctions and even supplying its erratic leader Kim Jong-un with fuel. There has been an increase in incursions in the far east of Russian this year by North Korean boats illegally fishing for squid and other fish in Russian waters, said Artyom Lukin, professor of international relations at the Far Eastern Federal University in Vladivostok. “The impact is made worse by North Korean poachers' wide use of drift nets that devastate marine wildlife,” he said. Russian authorities initially turned a blind eye to poaching by North Korean boats, Mr Lukin said, apparently to maintain friendly ties with Pyongyang. But the scale of the incursions has ruffled Moscow’s feathers. “It's clear the problem of North Korean fishing boats, hundreds of them, aggressively poaching in Russian waters, has become a major irritant in otherwise friendly Russia-DPRK relations,” he said. “It remains to be seen if and how it will be fixed.” In July, officials in Moscow accused North Korea of wrongfully detaining one of its fishing vessels and 15 Russian crew members. Pyongyang said the crew had been detained for violating the rules of entry into North Korea.