Paul Ryan announces candidacy for House Speaker
Paul Ryan speaks to CBS News (screen grab)

U.S. Republican congressman Paul Ryan formally announced his candidacy for speaker of the House of Representatives on Thursday after he nailed down crucial endorsements from Republican factions.

Ryan earlier this week said he was open to replacing retiring House Speaker John Boehner, but only if he could win the unified backing of his divided party colleagues in the House. By Thursday afternoon he had gathered support from conservative and moderate Republican groups.

"I believe we are ready to move forward as a one, united team. And I am ready and eager to be our speaker," Ryan wrote in a letter to fellow lawmakers. Republicans are scheduled to nominate a new speaker on Oct. 28, with a vote by the full House on Oct. 29.

(Reporting by Susan Cornwell; Editing by Sandra Maler)