The Russian parliament's lower chamber, the State Duma, has ratified agreements on the admission of the Luhansk, Donetsk, Kherson and Zaporizhzhia regions into the Russian Federation, news agency TASS reported on Monday.

Russian president Vladimir Putin on Sunday submitted draft federal constitutional laws to the State Duma on the admission of the new regions to Russia.

Russian Foreign Minister Sergei Lavrov addressed the parliament and congratulated representatives from the four regions and said he was confident the upper house of parliament would also approve the measures. 

The Kremlin said on Monday that it will consult with residents living in Kherson and Zaporizhzhia on how their borders should be defined. 

Ukrainian army advances in south

On the same day, Ukrainian troops recaptured villages along the west bank of the Dnipro River in southern Ukraine in a major new breakthrough. 

Kyiv gave no official confirmation of the gains, but a Russian official in occupied parts of Kherson province confirmed that Ukrainian army had captured a number of settlements along the river, pushing as far as the vicinity of the village of Dudchany. This would represent an advance of around 40 km in a single day. 

Balanced approach to nuclear weapon

The Kremlin on Monday said it favored a "balanced approach" to the issue of nuclear weapons, not based on emotion, after a close ally of President Putin called for the possible use of low-grade nuclear weapons. 

"In our country, the use of nuclear weapons happens only on the basis of what is stated in the relevant doctrine", Kremlin spokesperson Peskov said. 

According to the Russian nuclear doctrine, the use of nuclear weapons by Russia is possible if the enemy uses this or other types of weapons of mass destruction against Russia and its allies, or in the event of aggression against Russia with conventional weapons that endanger the very existence of the state. 

(With inputs from agencies)