MOSCOW (AP) — Russian President Vladimir Putin on Thursday ordered the Russian military to increase the number of troops by 137,000 to a total of 1.15 million amid Moscow’s military action in Ukraine.

Putin’s decree, which takes effect on January 1, didn’t specify whether the military will beef up its ranks by drafting a bigger number of conscripts, increasing the number of volunteer soldiers or using a combination of both. But some Russian military analysts predicted it would rely heavily on volunteers, a cautious stand reflecting the Kremlin’s concerns about a possible fallout from an attempt to increase the draft.

The presidential decree will boost the overall number of Russian military personnel to 2,039,758, including 1,150,628 troops. A previous order put the military’s numbers at 1,902,758 and 1,013,628 respectively at the start of 2018.

The Kremlin has said that only volunteer contract soldiers take part in what it calls the “special military operation” in Ukraine, rejecting claims that it was pondering a mobilisation.

Russian media and non-governmental organisations say Russian authorities have sought to bolster the number of troops involved in the military action in Ukraine by attracting more volunteers, engaging private military contractors and even offering amnesty to some prisoners in exchange for a tour of military duty.

Regional authorities have also tried to help beef up the ranks, forming volunteer battalions to be deployed to Ukraine.

All Russian men aged 18-27 must serve one year in the military, but a large share avoid the draft for health reasons or deferments granted to university students. The share of men who avoid the draft is particularly big in Moscow and other major cities.

The Russian military rounds up draftees twice a year, starting April 1 and October 1. Putin ordered the drafting of 134,500 conscripts during the latest spring draft earlier this year and 127,500 last fall.

In recent years, the Kremlin has emphasized increasing the share of volunteer contract soldiers as it sought to modernise the army and improve its capability. Before the Kremlin sent troops into Ukraine on February 24, the Russian military had over 400,000 contract soldiers, including about 147,000 in the ground forces. The number of conscripts has been estimated at around 270,000, and officers and non-commissioned officers have accounted for the rest.