Russia has expressed regret over its warplane violating South Korean airspace. According to Seoul's Presidential office, Russia has said that a military jet's intrusion into South Korean territorial airspace was not intentional and blamed a technical glitch. <br />''<br />''On Tuesday, Seoul said a Russian warplane had twice violated its territorial airspace. The Russian defence ministry had earlier denied this incident. But South Korea's Blue House said in a briefing that Russia had now said the violation was unintended and that it would immediately launch an investigation into the case. <br />''<br />''China's Defence Ministry today denied any of the planes had entered the territorial air space of any country. Russia's Defence Ministry had said its plane was taking part in a joint air patrol by Russian and Chinese warplanes over the Sea of Japan and the East China Sea – the first-ever air patrol between the two countries.<br />''<br />''Japan also has protested both to Russia and South Korea over the incident because it claims sovereignty over the islands.<br />