Congressional Budget Office warns of US debt default 'in first two weeks of June'

The nonpartisan Congressional Budget Office on Friday added more urgency to the fight over the debt limit, now saying there is a "significant risk" the U.S. will default on its debt "at some point in the first two weeks of June."

In a new report, the agency said "the extent to which the Treasury will be able to fund the government's ongoing obligations will remain uncertain throughout May, even if the Treasury ultimately runs out of funds in early June."

This is an escalation from agency's previous assessment of how soon the government won't be able to pay its bills. In a May 1 blog post, the CBO warned of a greater risk Treasury would run out of funds in early June, while in February the CBO targeted July as the month where the U.S. would no longer be able to meet its obligations.

Treasury Secretary Janet Yellen previously warned that a default could happen as soon as June 1, though Yellen has acknowledged there is considerable uncertainty around the exact "x-date."

The new CBO assessment underscores the tight timeline lawmakers are facing to reach a deal to lift the debt ceiling, or risk an unprecedented default that analysts have warned would wreak havoc on the economy.

President Joe Biden and congressional leaders ended this week with no solution after meeting at the White House on Tuesday for the first talks on the issue in months.

Staff for the leaders have been meeting daily since then to try to make progress, the White House said, while Biden and the "Big Four" -- House Speaker Kevin McCarthy, Senate Majority Leader Chuck Schumer, House Minority Leader Hakeem Jeffries and Senate Minority Leader Mitch McConnell -- are expected to meet again early next week.

The U.S. hit the debt ceiling in mid-January, and has since been using "extraordinary measures" to continue paying the government's obligations.

If the Treasury can continue financing the government through June 15, the CBO said expected quarterly tax receipts and other measures "will probably allow the government to continue financing operations through at least the end of July."

Yellen, appearing on ABC's "This Week" on Sunday, urged Congress to find a solution before Treasury runs out of tools to pay all its bills.

"We have been using extraordinary measures for several months now. And our ability to do that is running out," Yellen said. "And we will start to run down our cash and our current projection is that in early June a day will come when we’re unable to pay our bills unless Congress raises the debt ceiling."

-ABC News' Alexandra Hutzler contributed to this report.