MOSCOW, April 6 (Reuters) - The Kremlin on Wednesday defended its decision to station tactical nuclear weapons in Belarus, rejecting criticism of the move by NATO Secretary-General Jens Stoltenberg. Finland joined the NATO alliance on Tuesday, doubling the length of the alliance's land border with Russia, and Sweden is also set to join - moves triggered by Russia's despatch of its armed forces into neighbouring Ukraine last year. Russia has not given a clear timetable for moving tactical nuclear weapons to Belarus, but Putin said the construction of storage facilities should be complete by the start of July