U.S. municipal bond funds reported $2.22 billion of net outflows in the week ended June 19, up from outflows of $1.6 billion in the previous week, according to data released by Lipper on Thursday. The funds have had net outflows for four straight weeks, with the latest week the biggest since mid-December. For the four weeks outflows amounted to $5.4 billion. The four-week moving average remained negative at $1.36 billion, said Lipper, a unit of Thomson Reuters. Investors pulled out of high-yield funds for a fifth consecutive week, with net outflows of nearly $850 million, which was also the highest since the week of Dec. 19. In the week ended June 12, the funds reported outflows of $657 million. Exchange-traded muni funds saw outflows of $54 million in the latest week, up from $7 million in the prior week, according to Lipper. Meanwhile, retail investors bought 1.8 muni bonds for every one they sold in the week ended June 19, up slightly from a ratio of 1.7 the week before, acc