Ukraine is "fighting hard" against the ongoing Russian invasion, while the country's leader has also urged anyone with military experience to join the defence.
Russia launched a "full-scale invasion" on Wednesday morning, with blasts being heard and seen across widespread parts of Ukraine.
Fears are mounting that Russia's attack could instigate the biggest conflict seen in Europe since World War 2.
Speaking on Thursday morning, Mykhailo Podolyak, a Ukrainian presidential adviser, spoke out on the latest situation, before also confirming that there had already been civilian casualties.
"Our army is fighting back inflicting significant losses to the enemy," Podolyak said.
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Ukrainian tanks have been seen moving into regions
PA/CARLOS BARRIA
"Ukraine now needs a greater and very specific support from the world — military-technical, financial as well as tough sanctions against Russia."
Elsewhere, Oleksii Arestovich, an adviser to Ukrainian President Volodymyr Zelenskyy said that Russia had targeted air bases, as well as other military infrastructure.
"We suffered casualties, but they aren’t significant. (Russia) haven’t eroded the combat capability of the Ukrainian military."
Meanwhile, Zelenskyy has urged for anyone with military experience to join Ukraine's defence.
"Everyone who has military experience who can join the defence of Ukraine has to come to the military offices of the Ministry of Internal Affairs," he said.
"Please keep yourself updated on the information. We have wounded soldiers in hospitals that require blood donations, please join and donate your blood.
"We carry out serious work on the defence and every enterprise, every business person needs to help. Please look after your workers, your employees.
"All people should have all the necessary facilities and goods. The bank system of Ukraine has got the resources to protect this state, to protect the interests of Ukrainian nationals.
"I'm grateful to all the politicians who support Ukraine and defend our sovereignty."