WASHINGTON -- Democrats in the U.S. Senate increased their voting edge to 10 with a newly elected independent saying Wednesday he will align with them.

Senator-elect Angus King says he has decided to caucus with Democrats, ending months of speculation about which party he would vote with.

The former Maine governor was elected last week to replace retiring Republican Sen. Olympia Snowe, a prominent centrist. Republican and conservative groups spent millions of dollars to attack King during the campaign for Snowe's seat.

With King joining their caucus, Democrats will have a 55 to 45 edge when the new Senate takes office in January. The balance for the Democrats in the current Senate is 53-47. Republicans control the House of Representatives, meaning re-elected President Barack Obama will have to contend with a divided legislative branch.

King said Wednesday that caucusing with Democrats will still allow him to take independent positions on issues.

In the House, a congressional official said Democratic Leader Nancy Pelosi has told her party caucus she will remain as minority leader in the new session of Congress.

This official says the 72-year-old Pelosi made the decision to remain at the helm of the party's House leadership even though Democrats failed to win the necessary 25 additional seats to become the majority party again.

An official close to Pelosi revealed her decision on condition of anonymity because she hadn't yet publicly announced it.

Pelosi's quarter-century of service in Congress representing a San Francisco area district in the House includes becoming the first woman in history to serve as speaker. The conservative tea party-fueled political wave of 2010 forced the gavel from her hand to Rep. John Boehner, a Republican.