ATHENS – A deal led by US billionaire John Calamos to take over Ethniki Insurance, Greece’s largest insurer held by the Greek National Bank, looked to unravel after he sued its partner, the Dutch EXIN Financial Service Holdings for default on loans.

Calamos Family Partners said it had taken the action, announcing in an email statement that it wanted immediate repayment of more than $41 million in principal, plus interest, owed to them by EXIN under a series of loan agreements, the news agency Reuters said.

National Bank (NBG) had put its insurance subsidiary up for sale as part of a restructuring plan approved by the European Union to exit non-banking operations and focus on core banking but it had been lagging since being announced last year.

The takeover missed a Jan. 31 deadline to submit a list of stakeholders to the Bank of Greece amid reports a British fund could be brought in.

The Calamos-Exin group won a bid more than seven months ago but didn’t naming who will be involved to finance the deal, according to Kathimerini. The British fund manages one billion euros ($1.25 billion) and reportedly wants to put 300 million euros ($373.35 million) as a partner.

EXIN claimed it sent a full set of documents with the additional data it was asked for and that the deadline for the process is March 31, not Jan. 31, the paper said, adding that it was told by unnamed sources all the information isn’t available and that an EXIN email didn’t list the bank’s monitoring department of private insurance companies as a formal recipient.

The same sources further confirmed EXIN never submitted an integrated proposal presenting its stakeholder lineup but didn’t indicate whether the deal was in any danger of collapsing.

EXIN-Calamos came out as the winning bidder last year for Ethniki, reportedly offering between 700-750 million euros ($787.25-$843.49 million) for a 75 percent stake in the insurance arm, the country’s biggest insurer with an 18 percent market share.

Calamos is the owner of an asset management company whose CEO is fellow Greek-American John Koudounis.

Earlier, it was reported that the group wanted to bring in American investment mammoths Pimco and Warren Buffet’s Berkshire Hathaway,  one of the world’s richest man and a long-time financial sage, but could not confirm it and other reports denied Pimco’s interest.

Sources told the paper new funding vehicle then could also include the European Bank for Reconstruction and Development, though EBRD sources declined to comment.