MOSCOW (Reuters) - Expansion of NATO military infrastructure in Ukraine crosses a red line for Russian President Vladimir Putin, the Kremlin said on Monday, saying Russia and Belarus would act to protect their own security.

       Belarusian President Alexander Lukashenko earlier on Monday said he and Putin had agreed during talks to react to what he described as increased activity by NATO and U.S. troops in Ukraine.

       In particular, Lukashenko accused the U.S. of setting up military training centres in Ukraine which he said amounted to military bases.

       "(We) agreed that we need to take some kind of measures in response," Lukashenko was quoted as saying by the RIA news agency.

       (Reporting by Dmitry Antonov; Writing by Alexander Marrow; Editing by Andrew Osborn)