WASHINGTON, May 1, 2018 (Reuters) - US President Donald Trump has postponed the imposition of steel and aluminum tariffs on Canada, the European Union and Mexico until June 1, and has reached agreements for permanent exemptions for Argentina, Australia and Brazil, the White House said on Monday. The decisions came just hours before temporary exemptions from the tariffs on these countries were set to expire at 12:01 a.m. on Tuesday. In a statement, the White House said the details of the deals with Brazil, Argentina and Australia would be finalised shortly, and it did not disclose terms. "The administration is also extending negotiations with Canada, Mexico, and the European Union for a final 30 days. In all of these negotiations, the administration is focused on quotas that will restrain imports, prevent transshipment, and protect the national security," the White House added. A source familiar with the decision said there would be no further extensions beyond June 1 to stave off tariffs. Trump on March 23 imposed a 25 per cent tariff on steel imports and a 10 per cent tariff on aluminum, but granted temporary exemptions to Canada, Mexico, Brazil, the EU, Australia and Argentina. Trump has also granted a permanent exemption on steel tariffs to South Korea as part of a revision of a free trade pact that he sharply criticised.