US airline system traffic in June rose slightly after inching down in a month earlier, the U.S. Transportation Department reported on Friday. US airlines carried 66.6 million domestic and international passengers in June 2012, 0.6 percent more than the same period of 2011, said the department. The fresh number of passengers was also 2.5 percent above that of two years ago in June 2010. Specifically, there were 0.2 percent more domestic passengers and 2.8 percent more international passengers in June than a year ago. Southwest Airlines following its merger with AirTran carried more total system and domestic passengers than any other U.S. airlines in June, reaching 12.245 million and 12.116 million, respectively. United Airlines took the first place in terms of international passengers with as many as 2.3336 million. In the first half of this year, U.S. airlines carried 363.8 million passengers in total, up 1.6 percent from the same period in 2011. Suffering from economic crisis, the U.S. airline industry experienced sharp decline in flight demand. However, the nation's airline traffic has been gradually peaking up from the early 2010.