The death toll from clashes that erupted near the Ukrainian parliament building in central Kiev rose to three on Tuesday after two officers died in hospitals of wounds sustained in the violence, the country's authorities said.

The presidential aide Olga Bogomolets wrote on her Facebook page that a 21-year-old serviceman of the National Guard had died from massive blood loss, while another 20-year-old officer had passed away after his treatment for shrapnel wound to the brain failed.

Meanwhile, about 140 people, mainly law enforcement officers, remained hospitalized, the Interior Ministry said.

According to the statement on the ministry's website, two police officers, who were severely injured in a grenade explosion outside the parliament building, were hospitalized in intensive care in critical condition.

The tensions in central Kiev were fuelled as the parliament was due to vote on constitutional amendments on decentralization, which are expected to give more autonomy to Lugansk and Donetsk regions, controlled by independence-seeking insurgents.

The clashes started at about 10 a.m. local time (GMT 0700) when opponents of the decentralization plan attacked the police guarding the parliament building with smoke bombs and tear gas. Then they threw a hand grenade at the officers, which left an officer fatally wounded and dozens injured.

During the violence, 31 protesters were detained and 18 of them still remained in custody.

Constitutional amendments on decentralization are one of the main provisions of the Minsk peace deal signed in February, which is designed to put an end to the conflict in eastern Ukraine, which has already killed 6,800 people.

The changes of the country's constitution sparked a controversy in Ukraine with some political forces claiming that the move to grant more autonomy to certain regions could split the country apart.