US President Barack Obama is calling for the United States to make a new effort to ratify the comprehensive nuclear test ban treaty. Speaking in Prague, Obama said Sunday that ratification of the treaty that the Senate rejected a decade ago is one of the "concrete steps" the US can take to reach his goal of ridding the world of nuclear weapons. Over 140 nations have ratified the treaty, but 44 states that possess nuclear technology need to both sign and ratify it before it can take effect. Only 35 have done so. The United States is among the key holdouts, along with China, Egypt, India, Indonesia, Iran, Israel, North Korea, and Pakistan. Former President Bill Clinton signed the test ban treaty, but the Senate rejected it in 1999.