Russia's president Vladimir Putin on Wednesday warned Russia's foreign rivals against "crossing the red line" with Moscow, during a state of the nation speech. 

Putin told gathered lawmakers: "In some countries, they have started an obscene custom of blaming Russia for anything... It's some kind of sport, a new kind of sport." 

He added that Moscow wants "good relations" with all members of the international community, including those with which it does not see eye to eye. Ties between Russia and the West have deteriorated amid rising tensions over jailed Kremlin critic Alexei Navalny, a Russia troop build-up on Ukraine's borders and a series of espionage scandals. 

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His warning came just hours after Ukraine's President Volodymyr Zelenskiy signed a law allowing reservists to be called up for military service, without announcing mobilization. The law, which will make it possible to significantly boost the armed forces, was approved by parliament late in March and comes amid rising tensions with Russia in eastern Ukraine. 

"This will make it possible to quickly equip the military units of all defence forces with reservists, thereby significantly increasing their combat effectiveness during military aggression," the office said.

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Zelenskiy also challenged Putin on Tuesday to meet him in the Donbass region for talks to end the conflict and ease tensions between the neighboring countries. 

In the late evening video address, which comes following a flare-up in clashes, raising concerns of a major escalation in the war, Zelensky said: "Does Ukraine want the war? No! But is Ukraine ready for the war? Yes! Will Ukraine stop trying to achieve peace by diplomatic means? No, never! But, will Ukraine defend itself in case of something? Always! Our stand is simple: Ukraine never starts the war first, but Ukraine always stands until the end.

"Mr Putin, I'm ready to go even further and invite you to meet anywhere in the Ukrainian Donbas, where there is a war. Glory to Ukraine!"

There have been rising clashes and tension in the Donbass, where Ukrainian troops have battled Russia-backed forces in a conflict Ukraine says has killed 14,000 people since 2014. 

Ukraine, NATO and Western allies have said there is a "provocative" build-up of troops on Ukraine's eastern border and in Crimea. Russia says there is "provocative activity" involving the U.S. and NATO in the Black Sea region. 

On Monday, the EU estimated the number of Russian troops along the Ukrainian border is more than 100,000. During talks, Ukraine's foreign minister encouraged Western countries to hit Russia with a deeper package of economic sanctions in response to the conflict.

Video editor: Natália Luz