While a coalition agreement between the Centre Party, the Conservative People's Party of Estonia (EKRE) and Isamaa is already signed and ready to be implemented, the first attempt at forming a government is with Ms Kallas, as her party won the most mandates in the 3 March general election and President Kersti Kaljulaid thus gave her the task first.

Should Ms Kallas fail, outgoing Prime Minister Jüri Ratas (Centre) is likely to be the next candidate.

Reform-SDE coalition only possible if number of Centre, EKRE, Isamaa MPs bolt

Ms Kallas is faced with a difficult situation. Of the five parliamentary groups in the newly elected Riigikogu, the two she would like to see included in her government, namely that of her own party as well as that of SDE, only have 44 mandates. They may be able to win over Raimond Kaljulaid (independent), who, since he left the Centre Party in protest after it signed said coalition agreement with EKRE, is the new parliament's first independent member, but even that would bring them to just 45.

Centre-EKRE-Isamaa, on the other hand, at 56 mandates have a majority. Ms Kallas could be counting on some of those Centre Party MPs that over the last few weeks have expressed serious doubts in Mr Ratas' deal with Estonia's national-conservative and far-right parties.

Considering the extent to which the Centre-EKRE-Isamaa deal makes concessions in favour of Centre in terms of government positions, Ms Kallas told ERR last week that she will have to take it as it comes.

"Considering what [EKRE parliamentary group chairman] Martin Helme said in an interview, how Centre Party members needed to be promised positions in order for their attitude towards this coalition to be more positive, naturally I won't delude myself into thinking that they'll find the courage to vote their conscience," Ms Kallas said.

Kallas: Centre-EKRE-Isamaa coalition would be short-lived

Commenting on the real political perspective of a Centre-EKRE-Isamaa deal, Ms Kallas also said that current disagreements and mud-slinging in the media already suggests that such a government wouldn't make it to the end of the new legislative term.

"Coalitions last if the people involved in them get along," Ms Kallas said. "And from a distance, there's nothing like that to be seen at the moment. We're following what is going on, and we definitely plan to do our own work very well and also point to those problems."

Ms Kallas will hold a speech in the Riigikogu on Monday afternoon to introduce her own plan for a coalition, followed by the opportunity for other MPs to speak. She has said that rather than putting specific figures to a vote, she wants to outline the principles such a government would be based upon.

Should Ms Kallas fail, a vote on Mr Ratas' coalition is expected for late April.