SEOUL (Reuters) - North Korea fired at least one "unknown projectile" into the sea off its east coast, South Korea's military said on Thursday, in what would be the sixth round of missile tests this month.

       South Korea's Joint Chiefs of Staff said it had detected the launch, but did not elaborate.

       On Tuesday, North Korea had fired two cruise missiles into the sea off its east coast, South Korea's military said, amid rising tension over a recent series of weapons tests.

       Earlier in the month North Korea tested tactical guided missiles, two "hypersonic missiles" capable of high speed and maneuvering after lift-off, and a railway-borne missile system.

       (Reporting by Josh Smith; Editing by Chris Reese)