Czech President Milos Zeman says his office has received a threatening letter protesting his government's decision to help Kurdish forces in Iraq fight the Islamic State group.

Interior Minister Milan Chovanec says police experts are analyzing a white powder that was contained in the letter, which was delivered to Zeman's office on Wednesday.

Zeman, an outspoken critic of the Islamic State militants, was on a trip to the eastern Czech Republic at the time.

His country is not participating in the airstrikes that the U.S. and other countries are conducting against the Islamic State in Iraq and Syria. But the Czech Republic has sent the Kurdish military in Iraq 500 metric tons of ammunition and plans to help train Kurdish police there.