The U.S. Senate on Monday passed a bill on extending the current agreement with South Korea on civilian nuclear cooperation by two years.

The bill, effectively approved unanimously, authorizes President Barack Obama to extend the term of the nuclear energy agreement with South Korea until March 19, 2016.

Democratic Senate Majority Leader Harry Reid from Nevada declared the passage of the bill through the floor, citing no opposition from any senator.

Rep. Ed Royce, chairman of the House Foreign Affairs Committee, applauded the Senate's passage of the legislation.

"The U.S.-Republic of Korea (South Korea) relationship is a cornerstone of peace and security in the Asia-Pacific region," he said in a statement. "Extending the civil nuclear agreement strengthens this important relationship and is vital to our ally South Korea."

He is the author of a House bill on rolling over the nuclear agreement between the two nations, which passed unanimously in September.

Signed in 1974, the current version of the allies' nuclear energy partnership agreement is to expire in March.

The two sides have struggled to update the so-called 123 agreement amid Seoul's push to enrich uranium and reprocess spent fuel with Washington's consent.

Last year, Seoul and Washington agreed to extend the pact by two years in a bid to buy time for continued negotiations.

The senators have made a slight amendment to the House version, requiring the House to vote again.

"The House is expected to pass it as early as within this week," a diplomatic source said, adding the legislation will be immediately forwarded to Obama for his signature. (Yonhap News)