STORY: ::File 

A former Ukrainian energy minister has been detained, Ukraine's anti-corruption agency said on Sunday, as part of a major graft probe that sparked a political crisis last year.

The news comes as the country struggles to keep the heat on for its residents in the deep winter, amid Russian attacks targeting Ukraine's energy systems. 

The so-called "Midas" case centers on an alleged $100-million kickback scheme at the state atomic agency.

It has ensnared a number of senior officials and business elites, including a former associate of President Volodymyr Zelenskiy's.

The National Anti-Corruption Bureau of Ukraine said in a statement on Sunday, the former minister was detained while crossing the state border, and that it was within the framework of the 'Midas' case.

The agency did not name the individual and said more details would come.  

Ukraine's previous two energy ministers were forced to resign from roles in the government last November, amid the fallout from the scandal.

They have denied any wrongdoing.

Battling corruption is a key priority in Ukraine's reform effort as it eyes membership of the European Union.

On Saturday, Zelenskiy pushed again for a date for his country to join the EU, saying it was needed as part of security guarantees for a final peace package with Russia.

But at a panel on Sunday at the Munich Security Conference, the EU's foreign policy chief said she had a feeling that member states were not ready to set a concrete date.

Kaja Kallas said there was "a lot of work to be done," adding that the priority was for the EU to take action and show Ukraine is part of Europe.

Many EU governments say a fixed date is unrealistic, because EU accession moves forward only when there is progress in adjusting a country's laws to EU standards.