KYIV, Ukraine - Ukrainian President Volodymyr Zelensky on Wednesday signed a controversial law toughening punishments for disobedience or desertion from the armed forces amid Russia's invasion.

Stronger sanctions will also apply to offences such as threatening commanders, fleeing the battlefield, or consuming alcohol, according to the law published on the Ukrainian parliament's website.

The new law also prohibits courts from giving reduced or suspended sentences to soldiers found guilty.

Soldiers could face up to 12 years in prison for desertion, up to 10 years for disobedience or refusal to fight, and up to seven years for threatening a superior.

The text was criticised by human rights activists and some organisations had called on the president not to sign the measure, which was passed by parliament in December.

A petition against the law, published on the presidency's website in December, gathered almost 35,000 signatures.

"Instead of thanking soldiers, who have held off a full-scale Russian invasion for almost a year and successfully implemented operations to liberate the territory, we get jail time for the slightest disagreement or remark to commanders," the petition said.

The head of Ukraine's armed forces Valery Zaluzhny then defended the bill.

Zaluzhny said his position reflects that of "commanders of groups and military units who demanded a systematic solution to this set of issues" and that "in times of war, we need quick, effective solutions."

"The army is based on discipline. And if gaps in the legislation don't make sure (such discipline) is observed... this leads to an increase in losses," Zaluzhny said on Telegram.