Ukraine is rearming and deploying new units to the country's east to counter any attempt by pro-Russian rebels to take over more territory, President Petro Poroshenko has said.
Poroshenko said on Tuesday that the units would defend cities still under government control against possible incursions.
His remarks came after Ukrainian security officials claimed that Russia has intensified the transfer of troops and military equipment to separatist rebels, over the weekend. However, Moscow maintains that it does not aid the rebels.
"Several new units have been formed that will enable us to repel possible attacks in the direction of Mariupol and Berdyansk, Kharkiv, and areas north of Luhansk and the Dnipropetrovsk region," Poroshenko said, according to a statement on the presidential website.
Tensions have spiked since the weekend, when rebels held an election that was condemned by the West and Ukraine as illegal and destabilising.
Ukraine and Western governments say that Sunday's poll had gravely endangered the ceasefire that envisioned local elections across the whole of the east but under Ukrainian law.
Russia, however, quickly lent its support to the vote.
German Chancellor Angela Merkel, underlining her displeasure over what she said was Russia's role in the conflict, said on Tuesday there was no reason yet to lift European Union sanctions against Moscow.
Merkel said she hoped for a diplomatic solution to Ukraine's crisis but added the vote showed "how difficult it is even to maintain agreements that have been made, if we look at the illegal elections".
On Tuesday morning, the separatist leader in the Donetsk region, 38-year-old Alexander Zakharchenko was sworn in as head of the self-declared secessionist territory.
He was inaugurated in a heavily guarded theatre in the city of Donetsk, the main stronghold of a rebel-controlled territory that separatists call the Donetsk People's Republic.
Zakharchenko's election was largely a formality as no strong candidates opposed him, but the rebels say the vote gives them a mandate to pursue their secessionist goals.
The inauguration coincided with Russia's National Unity Day holiday, which saw rallies throughout the country, including one in Moscow.
The march in the centre of the capital included banners reading "Crimea is ours" - the Ukrainian region annexed by Russia in March - and "Novorossiya - we are with you."
The separatist Ukrainian regions are widely referred to by that name, which means "New Russia" and reflects the widespread opinion that eastern Ukraine is historically and ethnically part of Russia.
Source: Al Jazeera and agencies