The National Security and Defense Council did not specify if the leak was the result of a cyber attack, how much data was involved or who was responsible, Reuters said

But it said had "identified the vulnerability" and the portal,, had been secured. It gave no further details.

Ukraine and its institutions have repeatedly been the victims of cyber attacks, including an incident in February in which a virus was downloaded in a tax accounting program and spread to wreak havoc around the globe.

Read alsoBloomberg: U.S. spy agencies tracking Russian hack of Biden-linked Burisma

Kyiv this week asked the U.S. FBI for help investigating a suspected cyber attack by Russian military hackers on Burisma, an energy company caught up in the impeachment of U.S. President Donald Trump. Russia's defense ministry did not respond to a request for comment.

Meanwhile, the interior ministry announced an investigation into the possible illegal surveillance of former U.S. ambassador Marie Yovanovitch, following the release of text messages by the U.S. Congress as part of the impeachment case.

Illicit transmission of information has this week also impacted the highest levels of the Ukrainian government.

On Friday, President Volodymyr Zelensky asked law enforcement agencies to determine who was involved in making a secret recording in the office of Prime Minister Oleksiy Honcharuk.

Honcharuk offered his resignation after the recording suggested he had criticized Zelensky, whose office said measures should be found to improve ways of protecting information to avoid future such incidents.