In particular, they discussed "the possibility of jointly counteracting the construction of the Nord Stream 2 gas pipeline and popularising the capabilities of the Ukrainian gas transport system," the press service of the Ukrainian government said.

Ukraine and Estonia have friendly relations in economy, and bilateral trade has potential for growth, the Estonian president said. "I am optimistic about the development that is possible between our countries," she added.

Groysman stated that the Ukrainian government is currently actually building a new state — most spheres are being reformed. At the same time, he noted, all of these changes are taking place amid ongoing hybrid aggression.

"We once underestimated the threat Ukraine is now facing, but our current strategy is that we remain committed to European values and the policy of sanctions against the aggressor country," the Estonian president said.

Groysman later wrote on Facebook that he had many common topics to talk about with Kaljulaid — from countering Russia's hybrid aggression to the development of trade relations.

"Tallinn is interested in cooperation in information technology, energy efficiency and energy saving, in transportation, primarily in freight traffic," the Ukrainian prime minister wrote. "We are interested in increasing Estonian investment in the Ukrainian business sector, especially after the total amount of Estonia's investment in the Ukrainian economy last year exceeded $200 million."

Earlier on Tuesday, Kaljulaid met with Ukrainian President Petro Poroshenko. She is scheduled to return to Estonia on Sunday.