WARSAW (Reuters) - Poland has arrested a Russian citizen and charged him with espionage, a spokesperson for the Polish Minister Coordinator of Special Services said on Tuesday.

       Relations between Russia and countries once in the Soviet sphere of influence have long been fraught, but the invasion of Ukraine has increased suspicion about Moscow's intentions.

       The man had been living in Poland for 18 years and carrying out business activity. He was detained on April 6 and will be held in custody for three months, the spokesperson said in a statement.

       "The evidence gathered by the Military Counterintelligence Service indicates that the man, instructed by the Russian special services, collected information concerning the military readiness of the Polish Armed Forces and of NATO troops," he added.

       In March, Poland expelled 45 Russian diplomats suspected of working for Russian intelligence, and Moscow retaliated by expelling 45 Polish diplomats this month.

       (Reporting by Anna Wlodarczak-Semczuk; Editing by William Maclean)