WASHINGTON (AP) — President Donald Trump lashed out on Thursday at Republican leaders in Congress, suggesting efforts to increase the country's borrowing limit to avoid an economic-rattling default on the nation's debt are "a mess!"

On Twitter, Trump said he had asked Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan to attach legislation to increase the country's borrowing limit to a bill he recently signed related to veterans. Trump said they didn't do it and "now we have a big deal with Dems holding them up."

Raising the federal borrowing limit is a must-do item for Congress when they return to Washington from summer break. Congress faces an October deadline to increase the government's borrowing authority and avoid defaulting on U.S. obligations.

Adding to the complexity, Congress needs to pass stopgap legislation to avert a government shutdown when the budget year ends Sept. 30.

McConnell, at an event in Louisville, Kentucky on Thursday, did not respond to questions about Trump's comments. Ryan's office did not immediately respond to a request for comment.

Earlier this week, McConnell appeared in Kentucky with Treasury Secretary Steven Mnuchin, saying: "There is zero chance, no chance, we won't raise the debt ceiling."

The federal government has never before defaulted on debt payments. Financial experts have warned that default on U.S. bond payments could roil financial markets.

Trump's long-promised wall along the U.S.-Mexican border could complicate efforts to keep government running. Trump threatened Tuesday to force a federal shutdown unless Congress provides funds for the project.

White House counselor Kellyanne Conway stressed on Thursday the president was serious about moving forward with the wall.

Speaking on "Fox and Friends", Conway says Trump is "going to stick to building that wall and he wants the money to pay for it." She adds: "anybody who is surprised by that has not been paying attention for two years."

Trump again attacked McConnell on Twitter later Thursday morning over failed efforts to advance health care legislation. Said Trump: "The only problem I have with Mitch McConnell is that, after hearing Repeal & Replace for 7 years, he failed! That should NEVER have happened!"

The latest tweets from the president came a day after Trump and McConnell pledged to work together, amid reports of tension.

White House press secretary Sarah Huckabee Sanders said in a statement Wednesday that the two "remain united on many shared priorities," and they and other top officials will hold "previously scheduled meetings" after Congress returns from its August recess.

In his statement, McConnell said they have "a lot of work ahead of us, and we are committed to advancing our shared agenda together, and anyone who suggests otherwise is clearly not part of the conversation."

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Associated Press writer Adam Beam in Louisville, Kentucky, contributed to this report.