U.S. Treasury Secretary Steven Mnuchin said on Thursday that he wants to see "very significant" tax reform passed before Congress' August recess, but the Trump administration is still studying the merits of a proposed border tax system.

"We are committed to pass tax reform, it will be very significant, it's going to be focused on middle-income tax cuts, simplification and making the business tax competitive with the rest of the world," Mnuchin told CNBC in his first television interview since taking office last week.

"We want to get this done by the August recess," he added, acknowledging later on Fox Business Network that such a timeline was "very aggressive."

Mnuchin did not say when the plan would be rolled out. President Donald Trump has promised the announcement of a "phenomenal" plan by early March to cut business taxes, which helped push equity markets to record highs in recent weeks.

But some Republican senators have criticized a House Republican plan to levy a 20 percent tax on imports aimed at encouraging more U.S. production and exports and raising $1 trillion in revenue over a decade to offset lower business tax rates.

Mnuchin said the plan was still being studied.

"We're looking at it seriously, there are certain aspects of it that we're concerned about, there are certain aspects that we like," Mnuchin told Fox Business Network of the border tax adjustment plan. "It's going to be something that's focused on growth, and we will have listened to people's concerns and we will have taken them into account."

Mnuchin told both networks that he believed the tax reform plan would help the United States boost economic growth above 3 percent by late 2018 from 1.6 percent in 2016. Growth effects from tax reform and less business regulation would not likely start to take hold until next year, he added.

He told CNBC the Trump administration would use "dynamic scoring" models that would likely assume more growth than those assumed by Congress' Joint Committee on Taxation. This would have the effect of boosting assumed revenues from tax reform and relaxation of regulations.

Given the still-low interest rate environment he said it "makes sense" for the Treasury to examine whether to issue long-term debt of 50 to 100 years "at a very slight premium," but said he was not ready to make any announcements on this topic.

Mnuchin added to recent comments in the Wall Street Journal regarding the strong dollar, telling Fox Business Network that short-term increases in the dollar's value "are a reflection of the optimism of the economic plans" of the Trump administration.

Trump had pledged to declare China a currency manipulator on his first day in office, but Mnuchin told CNBC he would pursue the normal Treasury process of examining currency practices by major trading partners. Treasury is required by law to report on these findings by April 15.

He added that Treasury was also studying the effects of expanding the size of loans that the U.S. Export-Import Bank can make since it is currently limited by a lack of board members to loans under $10 million. He said the Trump administration was not interested in simply subsidizing large corporations.

This article was provided by Reuters.