WASHINGTON, April 26 (Xinhua) -- U.S. Treasury Secretary Steven Mnuchin confirmed on Wednesday that the administration proposes to cut the corporate tax rate to 15 percent from 35 percent in its long-awaited tax plan.

U.S. Treasury Secretary Steven Mnuchin speaks during a panel on 'Prospects for Tax Reform' at the Newseum, in Washington D.C., capital of the United States, April 26, 2017. U.S. Treasury Secretary Steven Mnuchin confirmed on Wednesday that the administration proposes to cut the corporate tax rate to 15 percent from 35 percent in its long-awaited tax plan.(Xinhua/Bao Dandan)

The tax proposal, which will be unveiled later in the day, would be the "biggest tax cut and largest tax reform" in U.S. history, Mnuchin said at an event hosted by The Hill.

"I think it's clear that the House, the Senate and the administration are all on the same page," he said, adding the administration wants a combined tax plan with Congress.

Mnuchin also confirmed that the infrastructure spending will not be included in the tax plan. "This plan is just tax reform," he said.

However, the details of a complete tax proposal probably won't be ready until June, according to Mick Mulvaney, director of the White House Office of Management and Budget.

"I think what you're going to see on Wednesday is some specific governing principles, some guidance. Also some indication of what the rates are going to be," Mulvaney told Fox News on Sunday.

"I don't think anybody expects us to rollout bill language on Wednesday. In fact, we don't want to do that," he said.

Amid concerns that large tax cuts would significantly increase U.S. fiscal deficits, Mnuchin on Wednesday reiterated that the administration will count on the compounding effect of strong economic growth over the next decade to finance the tax cuts.

However, many economists are skeptical about that argument, as the U.S. economic growth will average about only 1.9 percent over the next ten years, according to the nonpartisan Congressional Budget Office.

"You'd need about 0.9 percent additional growth over the 10-year budget window that is commonly used in Washington D.C. for budget bills. By 'additional growth,' I mean over and beyond what forecasters typically predict," said Alan Cole, an economist at the Tax Foundation.

"In order for a corporate income tax cut to 15 percent to be self-financing, it would have to raise the level of growth to 2.8 percent on average," he said.