Good news of a tentative deal for the U.S. debt ceiling impasse may quickly turn out to be bad news for financial markets.

U.S. President Joe Biden and top congressional Republican Kevin McCarthy on Saturday reached a tentative deal to raise the federal government's $31.4 trillion debt ceiling, two sources familiar with the negotiations said, potentially averting an economically destabilizing default.

But the deal still faces a difficult path to pass through Congress before the government runs out of money to pay its debts in early June.