As Russian President Vladimir Putin on Tuesday called for a halt to military action in eastern Ukraine, separatists from the self-proclaimed Luhansk People's Republic reportedly headed to Donetsk to provide reinforcements.
"Our troops have already been sent to Donetsk and Slovyansk. We are not only helping with equipment, but also with people," the head of the Luhansk republic, Valery Bolotov, told journalists on Tuesday, Rambler.ru reported.
Heavy fighting erupted in Donetsk late Monday, as pro-Russian separatists engaged in a shootout with Ukrainian troops at the city's airport.
Alexander Lyukyanchenko, the self-proclaimed mayor of Donetsk, said 40 people had been killed in Monday's violence, including two civilians, regional news outlet OstroV reported Tuesday.
The clashes did not go unnoticed by Russian leaders, with both Putin and Russian Foreign Minister Sergei Lavrov commenting on the intensified violence on Tuesday.
In a telephone conversation with Italy's prime minister, Putin stressed the importance of dialogue in resolving the ongoing conflict in Ukraine, according to a transcript posted on the Kremlin's website.
Lavrov told journalists at a news conference that the "number one task" of the authorities in Kiev should be "an immediate halt of military action against the population," Interfax reported.