Greek authorities hold another telephone call Tuesday with top international finance officials as Greece struggles to persuade lenders to grant it a loan installment to avoid default.

Finance Minister Evangelos Venizelos said his talks Monday with the European Union, European Central Bank, and International Monetary Fund were “productive and substantive.”

But before the telephone call, the IMF representative in Greece, Bob Traa, said Athens must quickly shrink the government, sell off some state-owned assets and improve tax collection. He warned of Greece going into default if it does not act quickly.

Venizelos promised the government would speed up reforms and lay off government workers. But he said the next few days would be “very difficult” for the country and the 16 other nations that use the euro currency.

Greece is facing default next month unless it can get the next installment of a $159 billion bailout from the EU and IMF. Greece is deep in debt. It has already cut spending and imposed new taxes to close its deficit, but has still fallen short of its budget targets. Creditors are demanding that Greece show it can meet their austerity demands before they release the next loan payment.

A Greek default could have devastating consequences throughout the entire European Union and the United States. The White House says U.S. President Barack Obama spoke to German Chancellor Angela Merkel by telephone Monday on the eurozone crisis. It says both agree that concerted action would be needed in the coming months to assure a global economic recovery.