Greece's government bonds slid, sending yields to a five-week high, on concern that a proposal to end financial aid from the International Monetary Fund early would allow the country to backslide on its budget controls.

Greek Prime Minister Antonis Samaras, whose country touched off Europe's debt crisis five years ago, is seeking to exit its bailout, which came with reform conditions that caused a political backlash.

"It must be a worrisome perspective to have Greece back on its own and Mr. Samaras trying to convince us that Greek debt is sustainable at current yield levels," said Marius Daheim, a senior fixed-income strategist at Bayerische Landesbank in Munich. "The market would be calmer if it knew Greece were to remain under an adjustment program with external control over economic policy and fiscal discipline."