The Kremlin said Tuesday that an order by President Vladimir Putin to transform Russia's army into the second largest in the world was needed to address growing threats on Russia's western borders and instability to the east.

Putin on Monday ordered the regular size of the Russian army to be increased by 180,000 troops to 1.5 million active servicemen in a move that would make it the second largest in the world after China's.

"This is due to the number of threats that exist to our country along the perimeter of our borders," Kremlin spokesman Dmitry Peskov told reporters on a conference call.

"It is caused by the extremely hostile environment on our western borders and instability on our eastern borders. This demands appropriate measures to be taken."

According to data from the International Institute for Strategic Studies (IISS), a leading military think tank, such an increase would see Russia leapfrog the United States and India in terms of the number of active combat soldiers it has at its disposal and be second only to China in size.

The move, the third time Putin has expanded the army's ranks since sending his military into Ukraine in February 2022, comes as Russian forces push forward in eastern Ukraine on parts of a vast 1,000 km (627-mile) frontline and try to eject Ukrainian forces from Russia's Kursk region.

Andrei Kartapolov, chairman of Russia's lower house of parliament's defense committee, said on Monday that part of the rationale for the expansion was to set up new structures and military units to improve security in the north-west of Russia after neighboring Finland joined the NATO alliance.

Russia has also expressed concerns about what it describes as the growing U.S.-backed militarisation of Japan and potential plans to deploy U.S. missiles there.