Fitch warned on Wednesday of a possible cut to the U.S. triple-A sovereign credit rating later this year if the ongoing government shutdown leads to it hitting its debt ceiling and hampering budget setting.

"If this shutdown continues to March 1 and the debt ceiling becomes a problem several months later, we may need to start thinking about the policy framework, the inability to pass a budget... and whether all of that is consistent with triple-A," Fitch's global head of sovereign ratings James McCormack said on Wednesday in London.

"From a rating point of view it is the debt ceiling that is problematic," McCormack added.

A shutdown of about a quarter of the U.S. government entered its 19th day on Wednesday, with lawmakers and the White House divided over Republican President Donald Trump's demand for money for a border wall.