Russian forces in Ukraine killed 12 people and struck energy infrastructure and a passenger train overnight on Tuesday, authorities said, days after negotiators from both sides held direct talks aimed at ending nearly four years of war.

In northeastern Kharkiv region, a drone hit a carriage of a train transporting nearly 200 passengers, killing at least five people, Ukraine's Prime Minister Yulia Svyrydenko posted on X.

"There is not and cannot be any military justification for killing civilians in a train carriage," Ukrainian President Volodymyr Zelensky said on Telegram.

Prosecutors posted images of the smouldering carriage on social media, which regional emergency services later said had been extinguished.

A barrage of more than 50 Russian drones killed three people and wounded more than 30 in the southern city of Odesa, regional officials said.

The Black Sea city key for Ukrainian exports has been routinely pummelled by Russian forces.

Regional governor Oleg Kiper said a woman, 39 weeks pregnant, and two girls were among the wounded.

An AFP journalist at the scene saw the collapsed facade of a residential building and rescue workers searching the rubble for victims.

Zelensky said the bombardment undermined peace efforts and urged allies to step up pressure on Moscow to end the war.

"Every such Russian strike erodes the diplomacy that is still ongoing and undermines the efforts of partners who are helping to end this war," he wrote on social media.

Deadly strikes on energy infrastructure that have left many Ukrainians without power in freezing temperatures have continued since Russian and Ukrainian negotiators met in the United Arab Emirates last week for US-brokered talks aimed at ending the conflict.

The next round is expected to take place on February 1, according to Zelensky.

Millions without power
Ukrainian private energy firm DTEK said Russian forces had inflicted "enormous" damage on one of its facilities in the Odesa region overnight.

Kiper said dozens of residential buildings, a church, kindergarten and schools had been damaged in the attacks.

A married couple aged 45 and 48 were killed in Sloviansk in the eastern Donetsk region, which the Kremlin claims to have annexed. Their 20-year-old son survived the attack, local prosecutors said.

In the southern region of Zaporizhzhia, a 58-year-old man was killed in a drone attack. A 72-year-old was killed in her home by Russian shelling in the southern Kherson region.

Russian drone and missile attacks have knocked out power, lighting and heat to millions of Ukrainians across the country.

The Ukrainian air force said Russia had launched 165 attack drones overnight, and officials said an infrastructure facility in the western Lviv region was hit.

State gas company Naftogaz said the attack had left one of its facilities on fire in western Ukraine, describing it as the fifth attack of its kind this month.

Russian forces are slowly advancing across the front. The Russian defence ministry announced on Tuesday it had captured two more villages in the Zaporizhzhia and Kharkiv regions.