The stock markets in the United States declined due to investors' concern regarding the potential exit of Greece from the European region. The equity markets in the Asia-Pacific and Europe also declined. Sign up for our free newsletter Investors were concerned regarding the possibility that Greece will not be able to repay the $1.8 billion due to the International Monetary Fund IMF on Tuesday. Commenting on Greece's situation, Michael James, managing editor of equity trading at Wedbush Securities told Bloomberg, "We finally reached the breaking point. With so much uncertainty around a potentially negative outcome, the knee-jerk reaction will be to reduce risk assets. You have a potentially very ugly situation this week." In Greece, banks and markets were closed after Prime Minister Alexis Tsipras interrupted the final debt negotiation early Saturday. He called for a July 5 referendum whether to accept the terms of the financial aid package offered by its international creditors. Mark Haefele, a global chief investment officer at UBS Group commented, "The Greek tragedy opened a new act over the weekend. He thinks that Greece will remain in the Eurozone, but the lack of resolution is creating a market volatility. Leon Cooperman of Omega Advisors said he sees a 50% chance for Greece to exit the Europen region. Meanwhile, the National Association of Realtors NAR reported that the sales of existing homes increased 5.1% to a seasonally adjusted annual rate of 5.34 million in May. NAR Chief Economist Lawrence Yun said, "May home sales rebounded strongly following April's decline and are now at their highest pace since November 2009. Solid sales gains were seen throughout the country in May as more homeowners listed their home for sale and, therefore provided greater choices for buyers."