The dollar strengthened to a four-week high against the euro following comments from U.S. Federal Reserve Chair Janet Yellen on May 22 that it would be “appropriate” to raise interest rates this year if the economy improves. Iraq’s prime minister pledged a swift recapture of the city of Ramadi from Islamic State militants, while in Saudi Arabia King Salman vowed to punish those responsible for a suicide attack on Shiite worshipers.