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Malgorzata Gosiewska, a member of parliament from Poland's ruling conservative Law and Justice (PiS) party, headed a Polish delegation to war-torn Avdiyivka in the eastern Donbas region of Ukraine, according to the defense ministry in Kyiv, Radio Poland wrote.

"We must remember that the war in eastern Ukraine is taking place quite near [to Poland]," Gosiewska said, according to the wschodnik.pl website.

She said she was "impressed by the way Ukraine had united to support Avdiyivka's citizens," adding that only joint multinational efforts could put an end to the fighting in Ukraine's east.

Read alsoATO HQ: Truce disrupted, no conditions for withdrawal of armsMeanwhile, Reuters reported that a ceasefire has been in place since 5pm on Sunday after leaders of Germany, France, Russia and Ukraine agreed to implement the terms of a 2014 peace agreement which had been violated in the past.

Under the new ceasefire deal, both sides were to simultaneously withdraw their heavy weapons on Monday.

Read alsoNearly 10,000 people killed in Ukraine in three years of Russian aggression – ministryGosiewska is a co-author of report entitled "Russian Crimes in the East of Ukraine," which was last year submitted to the International Criminal Court in the Hague.

She is the first wife of the late Przemyslaw Gosiewski, also a PiS MP, who died along with 95 others, including then-President Lech Kaczynski, when a Polish presidential plane crashed while trying to land in fog in Smolensk, western Russia in 2010.

Some 10,000 people have died in the conflict in eastern Ukraine, which started in April 2014.