UPDATE 1-FCC approves merger of T-Mobile, Sprint on vote split on party lines

(Adds details of the merger)

WASHINGTON, Oct 16 (Reuters) - T-Mobile US Inc's proposed $26.5 billion tie-up with Sprint Corp won formal approval from the Federal Communications Commission on Wednesday in a vote split along party lines, two sources told Reuters.

Chairman Ajit Pai and two Republican commissioners voted to approve the deal while two Democratic commissioners voted against it, the sources said.

The text of the approval order is not expected to be released until later in the month.

The deal to combine the third and fourth largest U.S. wireless carriers, which has been fighting for government approval since April 2018, still faces a lawsuit brought by a group of state attorneys general, headed by New York. (Reporting by David Shepardson; writing by Diane Bartz; Editing by Lisa Shumaker)