The Kremlin says the four regions of Ukraine that held referendums on joining Russia will be incorporated into the country on Friday.
So-called votes were held in Luhansk and Donetsk in the east, and in Zaporizhzhia and Kherson in the south and have been denounced by Ukraine and the west as a sham.
Kremlin spokesman Dmitry Peskov said that Russian President Vladimir Putin will attend a ceremony in Moscow at which they will be officially folded into Russia.
Mr Peskov told reporters on Thursday that the heads of the four regions where the five-day voting wrapped up on Tuesday will sign treaties to join Russia during Friday's ceremony at the Kremlin's St George's Hall.
Following the signing ceremonies, Mr Putin will give a major speech and meet with Moscow-appointed administrators of the Ukrainian regions. A celebratory concert on Red Square is planned for Friday evening and Mr Peskov said the media would be informed later on whether Mr Putin would attend.
Ukraine’s President Volodymyr Zelensky issued a new warning to Russia of a “very harsh” response if Moscow goes ahead with the annexations.
A statement issued by Mr Zelensky’s office after a telephone call with Italy’s prime minister did not refer to the ceremony on Friday.
“They (the votes) are worthless and do not change reality. The territorial integrity of Ukraine will be restored. And our reaction to recognition of the results by Russia will be very harsh,” Mr Zelensky said.
Meanwhile, Finland says it will ban most Russian tourists from entering the country, starting on Friday.
Foreign minister Pekka Haavisto said during a news conference that: “The decision in principle aims to completely prevent Russian tourism to Finland and the related transit through Finland.”
Mr Haavisto cited security concerns related to Russia's war in Ukraine, the “illegal” referendums arranged by Russia and recent leaks in the Nord Stream pipelines as events that led to the decision.
Russians can still enter Finland, which shares a 1,340-kilometer land border with Russia, for family reasons, for study or work purposes. Also, Russian political dissidents may seek to enter the country for humanitarian purposes.
Mr Haavisto had earlier said he was particularly worried about a kind of Russian “tourist route” through Helsinki airport which was used by thousands of Russians before Ukraine was invaded.
Until now, Russians have been crossing into Finland before flying to other European nations as a way of circumventing flight bans imposed after the invasion.
