The Bulgarian prosecutor's office will investigate allegations of bribery in the attempted sale of the bankrupt Chimco Vratsa fertiliser plant.

Jan Aronov, president of US-based ANJ Group Corp, which was interested in acquiring the assets of the plant last year, claims that a bribe was requested and accepted by the assignee of the bankrupt factory.

In a letter addressed to Prime Minister Boyko Borisov, Aronov claims that EUR 15 000 were paid in cash to the assignee of the factory during a visit to the plant.

During one of the meetings at which the sale of the assets were discussed, a representative of the assignee, who presented himself as a partner of the incumbent prime minister, said that the contract will not be signed unless a cash payment of EUR 500 000 is made.

The representative promised that upon receipt of the payment the contract will be signed on the following day.

He also requested for another payment of EUR 500 000 generated from the activities of the plant to be made in the future.

Aronov claims to have sent a copy of the letter to Chief Prosecutor Sotir Tsatsarov and Charge d'Affaires at the US embassy in Sofia Martina Strong. The latter, however, is quoted by the news website Dnevnik.bg as saying she has not received any letter by Aronov.

"My representatives were left with the impression that a criminal gang is being formed around the sales of the assets of Chimco whose goal is to blackmail potential investors".

Aronov is calling on the government to intervene and "stop the activity of this group".

"I am begging you to help us in the project crucial to the economy of Bulgaria," he says in the letter which the government's press office says has not been edited by its staff.

Earlier, the cabinet stated that "neither as of September 08, 2015 - the date pointed in the letter by Mr Aronov - nor as of today the Prime Minister as an advisor [sic!] with the name in the letter - "Mr Bogdanov".

The Bulgarian prosecution and the State Agency for National Security (DANS) have started investigation into the allegations.

This comes days after it emerged that the plant will be acquired by a company owned by controversial MP and media mogul Delyan Peevski.

His company was the sole participant in the tender for the sale of the plant.