WASHINGTON (Reuters) - The U.S. Senate on Tuesday rejected an effort to require an international nuclear agreement with Iran to be considered a treaty, which would have forced any deal to be approved by two-thirds of the Senate's 100 members before it could take effect.

The Senate voted 57-39 to reject the measure, offered as an amendment to a bill requiring an Iran nuclear deal to be reviewed by Congress.

The amendment would have needed the support of 60 senators to pass, but its support from 39 Republicans showed that there could be intense debate in the coming days as the Senate agrees on a final version of the legislation.

Senator Majority Leader Mitch McConnell and other members of the chamber's Republican leadership were among those who supported the amendment, despite an emotional appeal against it from Senator Bob Corker, the Republican chairman of the Senate Foreign Relations Committee and author of the Iran Nuclear Review Act.