In an email to Mr Ratas, Mr Verhofstadt, a former prime minister of Belgium, stated that EKRE was an "extreme right-wing political party which resembles European fascist regimes", according to the European arm of the Politico journalism outlet, which has obtained a copy of the email.

A Centre-EKRE cooperation would be "detrimental to Estonian society and the country's geopolitical position and cause irreparable damage to our excellent cooperation in a liberal family," the email reportedly went on.

Ratas: Brussels shouldn't dictate makeup of coalition

In response to Mr Verhofstadt's email, Mr Ratas said that Brussels should not be dictating anything to Estonia.

"We have been in touch with quite a few ALDE prime ministers, and they have expressed supportive messages," the current prime minister told ERR on Thursday. "I believe that Brussels should not dictate to Estonia now what our new coalition will be. The people of Estonia, our highest authority, have demonstrated what kind of XIV Riigikogu they wish to see, and we are acting according to what the people of Estonia have said."

Talks continue

Centre is on day two of talks with EKRE, as well as conservative party Isamaa, after rejecting a coalition talks offer from the Reform party at the end of last week. A Centre-EKRE-Isamaa coalition would have 57 seats, above the 51 seats required for a Riigikogu majority.

Reform has the largest number of seats for a single party at 34, following the 3 March general election, but an alliance with the only other elected party left, the 10-seat Social Democratic Party (SDE), would not be enough for a Riigikogu majority.

Reform's leader Kaja Kallas was formerly an MEP and sat with the ALDE fraction in the European Parliament, as do Centre MEPs.

There is a total of 68 MEPs sitting with ALDE in the (pre-Brexit) 751-seat European Parliament at Strasbourg.

EKRE has been widely reported in the international media as a far-right party. It takes a firm stance against the UN Global Compact on Migration, as well as being strongly Eurosceptic. It is also described by some as neo-Nazi, though its official platform lacks obvious irredentist, anti-Slavic or anti-Semitic themes, and it does not have a paramilitary wing as such.

Centre is, as its name suggests, a centrist party, often described as populist. It is somewhat fragemented in its internal membership, most noticeably in municipalities where it predominates, such as the eastern Estonian city of Kohtla-Järve. Traditionally it drew a lot of support from the Russian-speaking minority in Estonia, something which has declined more recently as the party has sought to move beyond the legacy of founder member, Edgar Savisaar. It broadly has some commonalities with EKRE on the issue of language in education, for instance (and is opposed to Isamaa in this area) and differences on others, for instance on the issue of same-sex cohabitation or marriage.