Ukrainian security agents on Monday seized documents from the Kiev branches of Italy's UniCredit bank as part of an anti-terror investigation linked to individuals with accounts in the European giant.
A spokeswoman for Ukraine's State Security Service (SBU) told Interfax the snap inspections were conducted "in order to halt possible operations aimed at financing terrorist organisations" in the separatist east.
Ukraine calls its 13-month war with pro-Russian rebels an "anti-terrorist operation" and probits financial or other links with the leaders or field commanders of the self-proclaimed Lugansk and Donetsk "people's republics".
SBU spokeswoman Olena Gitlyanska stressed that authorities had no problems with the bank itself.
But UniCredit's Ukrainian office complained that the bank had been cooperating closely with the security service and saw no reason why investigators would effectively shut it down for a part of the day.
"The bank provided all the requested information, cooperating with the investigation to the utmost," a bank spokeswoman said in a statement.
"However, SBU agents decided to block our branches' operations by restricting the movement of its personnel, and through other measures."
Kiev's 112 television channel said the SBU was particularly interested in one person who had opened three accounts at the bank.
UniCredit's Ukrainian division was established in 1997 and is currently one of the largest financial institutions in the ex-Soviet state.