European Union (EU) leaders agreed early Thursday morning a long-awaited deal on combatting the ongoing debt crisis, under which private creditors will write off 50 percent of the value of the Greek bonds they hold.

"We have reached a sustainable solution for Greece," said European Council President Herman Van Rompuy at a press conference held after a prolonged eurozone summit which dragged from Wednesday evening to Thursday morning.

Under the eurozone summit deal, a new EU-International Monetary Fund (IMF) program of up to 100 billion euros (137 billion U.S. dollars) will be put in place by the end of the year for Greece to help Greece reduce its public debt to 120 percent of its gross domestic product (GDP) in 2020.

To reach the goal, "a voluntary contribution by private creditors who had lent to Greece" is needed, and the private holders of the Greek debt have agreed to take a nominal discount of 50 percent on notional Greek debt, Van Rompuy told reporters.