South Korea remains vigilant against additional North Korean provocations, such as a long-range missile launch or a nuclear test, following a series of recent missile firings, Seoul's defense chief said Wednesday. In a report to the National Assembly, Defense Minister Kim Kwan-jin said Pyongyang fired short-range missiles to raise tensions in a show of force against military exercises between South Korea and the United States that have been underway since last week. "It is different from a one-time firing," Kim said during an emergency meeting of the parliamentary defense committee. "Unlike in the past, the North intensively fired various projectiles in a short period of time."    Over the past week, Pyongyang has fired Scud missiles and short-range projectiles using multiple rocket launchers with varying ranges from its eastern coast, despite Seoul's warning to stop provocations. Kim, who had earlier predicted the communist state may provoke the South between January and March, said the North could launch large-scale attacks depending on the state of inter-Korean relations. "I don't exclude the possibility of the North conducting additional long-range missile launches or a nuclear test," Kim said, noting that the South Korean and U.S. forces have stepped up surveillance status to prepare for contingencies. Pyongyang launched a long-range rocket in December 2012, and conducted its third nuclear test in February 2013, bringing a wave of international sanctions on the isolated communist regime. Also on Wednesday, Seoul's defense ministry denounced Pyongyang for firing short-range rockets without designating a no-fly zone, saying such an act seriously threatened a Chinese airline that was passing near their trajectory. Pyongyang fired a total of seven short-range projectiles from its southeastern coast on Tuesday -- three in the morning and four in the afternoon. Seven minutes after one rocket was launched at 16:17 p.m., a Chinese airline heading from Japan's Narita International Airport toward Shenyang in northeast China passed through the trajectory of the rocket, the ministry said. The rocket flew about 155 kilometers in the northeast direction from the North Korean city of Wonsan on the east coast. "North Korea's provocative act violates the international aviation regulations, while seriously threatening the safety of civilians," ministry spokesman Kim Min-seok said. "We urge (the North) to stop provocative acts and abide by international regulations."    Meanwhile, a spokesman for the North Korea's Strategic Rocket Forces said Wednesday it successfully carried out military drills from Feb. 21 to March 5 for the purpose of "self-defense,"stressing that the drills were legitimately held in its own territory. The spokesman blamed Seoul and Washington for raising tensions on the peninsula by holding the Key Resolve exercises, calling them "provocations."    "The U.S. and its followers should keep in mind that if their provocations go too far, the purpose of the rocket drills can turn from self-defense to retaliation," the spokesman was quoted as saying by the state-run Korean Central News Agency.