EU governments threatened sanctions against Turkey on Friday over its offensive in Syria, angrily rejecting President Tayyip Erdogan's warning that he would "open the gates" and send 3.6 million refugees to Europe if they did not back him.

Turkey has stepped up its air and artillery strikes on Kurdish militia in northeast Syria, escalating an offensive that has drawn warnings of a humanitarian disaster and also raised the prospect of new U.S. sanctions on Ankara.