WASHINGTON (Reuters) – The United States conducted three “successful self defense strikes” against Houthi targets in Yemen on Friday, the White House said. White House spokesperson John Kirby said this was the fourth pre-emptive strike in the past week by the U.S. military against Houthi missile launchers that were prepared to launch attacks. “These actions were, I want to stress again, done in self defense, but it also helps make safer international waters for both naval vessels as well as … merchant shipping,” Kirby said. The Iran-backed Houthi militia launched two anti-ship ballistic miss…