Republican U.S. presidential candidates on Wednesday faulted President Barack Obama's "feckless" and "failed" foreign policy for letting North Korea bolster its nuclear arms capabilities, while also blaming Democratic front-runner Hillary Clinton.

The Republicans, who often criticize Obama's handling of foreign affairs, including Syria's civil war, the rise of Islamic State and the agreement to curb Iran's nuclear program, made their comments after North Korea said it tested a miniaturized hydrogen nuclear device on Wednesday. The United States expressed doubts about North Korea's claim.

Clinton, who served as Obama's secretary of state from 2009 to 2013, condemned North Korea's move as a "dangerous and provocative act" and said the United States should respond with more sanctions and stronger missile defenses. She also defended her performance as Obama's top diplomat.