U.S. President Barack Obama on Monday expressed his support for Greece to remain in the euro zone, saying world leaders have "indicated their desire to see Greece in the euro zone."

"I think it's important for Greece to work through what their options are at time of great difficulty," Obama told a press conference by the end of two-day NATO summit.

"I'm not going to speculate on what happens if the Greeks choose to exit (the euro zone), because they've got an election and this is going to be an important debate inside of Greece," he said.

Obama said what happened in Greece has impacted the United States, as businesses were more hesitant to invest amid uncertainty looming across the Atlantic. "They're not sure whether that's going to mean a further global slowdown."

"We've got to put in place firewalls that ensure countries outside of Greece aren't harmed just because markets are skittish and nervous," the president said. "We've got to make sure that banks are recapitalized in Europe so that investors have confidence."

Greek conservative parties recently demanded renegotiating part of the harsh austerity terms of the two bailout deals clinched with the EU and IMF lenders in a bid to ease the burden off the Greeks and secure the future flow of vital multi-billion euro loans to avoid a disorderly default and possible exit from the euro zone.