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

Putin’s decree, which takes effect on Jan. 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.

The presidential decree will boost the overall number of Russian military personnel to 2,039,758, including 1,150,628 servicemen. 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 broad mobilization.

Russian media and non-governmental organizations 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 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 Oct. 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 modernize the army and improve its readiness. Before the Kremlin sent troops into Ukraine on Feb. 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.

Military observers have noted that if the campaign in Ukraine drags on, those numbers could be clearly insufficient to sustain the operations in Ukraine, which has declared a goal of forming a 1-million-strong military.

Retired Col. Viktor Murakhovsky noted that Putin’s decree on Thursday reflected the pressure of filling the ranks amid the military action in Ukraine.

In comments carried by the RBC online news outlet, he charged that the Kremlin would likely try to keep relying on volunteers and predicted that they would account for the bulk of the increase ordered by the Kremlin.