BUCHAREST (Reuters) -Romanian anti-corruption prosecutors asked parliament and the president on Thursday to allow a criminal investigation into former prime minister Florin Citu and two former ministers for suspected abuse of office concerning COVID-19 vaccine purchases.

That coalition collapsed after less than a year in power, at the height of the coronavirus pandemic, and was replaced by the current government of Liberals and leftist Social Democrats.

Prosecutors want to investigate Citu, Voiculescu and Mihaila for allegedly purchasing significantly more Pfizer and Moderna vaccine doses than necessary during January-May 2021 without documents or assessments to justify the purchase.

Prosecutors said that although Romania had already purchased 37.6 million doses prior to Jan. 2021 - enough to vaccinate all Romanians - the three cabinet members agreed to buy an additional 52.8 million doses which cost the state budget a little over 1 billion euros ($1.09 billion) before VAT.

Citu and the former ministers denied any wrongdoing.

"I fully trust the justice act and I am convinced the ongoing procedures will uncover the truth," Citu said in a Facebook post, adding that he has always respected the law.

In a separate Facebook post, Voiculescu said the purchase decisions were exclusively made by the prime minister but added the number of doses "was a decision taken under uncertain conditions regarding availability of supply, developments of the virus strain and the need for boosters."

Under Romanian law, prosecutors need parliament's and the president's approval to investigate and detain sitting lawmakers and former cabinet ministers for graft offences allegedly committed while they were in office.

Lawmakers have a patchy record of approving such requests, but Citu has been a vocal critic of the current coalition government which includes his party, ahead of local, European, general and presidential elections in 2024.

Romania is the European Union's second-least vaccinated state after Bulgaria, plagued by distrust in state institutions and poor vaccine education. World Health Organization data showed the virus has killed 68,590 people to date in the country of 20 million.

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(Reporting by Luiza Ilie; editing by Christina Fincher and Deepa Babington)