Pope Francis on Sunday announced that a special collection would be taken up in all of Europe's Roman Catholic churches on April 24 to raise funds to help the people of Ukraine.
Speaking to tens of thousands of people at the end of a Mass in St. Peter's Square, he said he wanted the collection to be a "gesture of charity that, apart from alleviating material suffering, shows my personal closeness as well as that of the entire Church" to the people of Ukraine.
Violence has intensified recently in eastern Ukraine between government forces and Russian-backed rebels, international monitors have warned.
Implementation of a deal agreed in Minsk last year, which would allow for the lifting of sanctions on Russia, and a lull in violence late last year had raised hopes that the conflict that has killed more than 9,000 people could be resolved soon.
The vast majority of Christians living in Ukraine are Orthodox but there are about a million Roman Catholics and about four million Eastern Rite Catholics who are in unity with Rome.
The pope did not say how the aid would be distributed. There are about 120,000 Roman Catholic parishes in Europe, with the largest number - about 27,000 - in Italy.