China said on Tuesday it was concerned about reports that a U.S. aircraft carrier may join a military exercise with South Korea amid a tense standoff with North Korea over the sinking of a warship from the South. Chinese Foreign Ministry spokesman Qin Gang said he had seen the reports about the U.S. aircraft carrier joining the drill. "We're extremely concerned about these reports and will closely follow developments," he told a news conference. He said China was worried the show of naval force could unsettle the region. "Under current circumstances, all the parties concerned should exercise calm and restraint and do nothing to escalate tensions and harm the interests of countries in this region," Qin said.