Turkish President Tayyip Erdogan said on Thursday that his country would soon close its border with northern Iraq and shut its air space in response to last week’s Kurdish independence referendum.

According to Reuters, Erdogan said the decision to hold the referendum showed the “perfect ingratitude” of the Kurdish Regional Government in northern Iraq, which had developed close commercial and political ties with Turkey.

“Flights to northern Iraq have already been suspended, the air space and borders will also close soon,” Erdogan said in a speech in the Turkish capital, Ankara.

“We demand the KRG take the necessary lesson from their mistakes and take steps to compensate for them as soon as possible,” Erdogan said.

On the other hand, Iraq’s central bank on Wednesday eased financial restrictions imposed on the Kurdistan region over its independence vote after receiving a pledge of cooperation from Kurdish banks, an Iraqi banking source said.

All but four Kurdish-owned banks were allowed to send and receive dollar and foreign currency transfers on Wednesday, the source told Reuters.

It is the first de-escalation measure in the crisis, which erupted after voters in the Kurdish region of northern Iraq overwhelmingly backed independence in a Sept. 25 referendum.

The Iraqi government has also imposed a ban on direct international flights to and from the Kurdish region.

The central bank had informed the Kurdistan Regional Government (KRG) on Tuesday it would stop selling dollars to the four Kurdish banks, and would halt all foreign currency transfers to the autonomous region, banking and government sources told Reuters.

The measures are aimed at tightening the central bank’s control over the Kurdish banking industry.

The central bank will maintain its dollar sale ban for four of the Kurdish banks pending a review of their cooperation, the banking source said.