"We have an S-400 division there," said General Nikolai Makarov, chief of staff of the Russian armed forces, confirming that Russia had deployed its most advanced anti-missile defence system near the border with North Korea.
"We are indeed worried about the way testing, including tests of nuclear devices, is being conducted in North Korea," said Makarov, who was accompanying President Dmitry Medvedev on a visit to Mongolia.
"This is happening very close to Russia's borders. We will take certain steps to guard against the possibility of a missile falling" on Russian territory, he told journalists in the Mongolian capital.
In addition to deployment of the S-400 unit, Makarov said Russian defence chiefs were weighing further steps to make sure no North Korean missiles, or pieces of missiles, landed in Russian territory.
"We are now reviewing what more effective steps can be taken to guarantee no rocket fragments fall in the event of a faulty launch."