U.S. lawmakers narrowly approved legislation key to securing a hallmark Pacific trade deal on Thursday, partly reversing a defeat less than a week before, in a boost to President Barack Obama's goal of strengthening U.S. economic ties with Asia.

The House of Representatives voted 218 to 208 to give the White House authority to close trade deals such as the 12-nation Trans-Pacific Partnership (TPP), which encompasses 40 percent of the global economy and is close to completion.

But the bill, a stripped-down version of legislation that failed at a vote last week, must now go back to the Senate for approval, and passage is not assured.