North Korea seems to be preparing to test-fire several medium-range missiles from its southeast coast, South Korea's Yonhap news agency reported Tuesday. At least three missiles are apparently being prepared for launch from a missile base in Anbyon County, about 100 kilometres (60 miles) northeast of Seoul, Yonhap said. It said that several vehicles mounted with mobile launch pads were spotted at the base. 'At least three missiles are expected to be fired,' a government source told Yonhap. The missiles are believed to include a Rodong with a range of 1,300 kilometres or a new medium-range missile with a range of 3,000 kilometres, it said. The South's defence ministry said it could not confirm the report. The North has launched a series of short-range missiles since its second nuclear test on May 25. US and South Korean officials have said there are signs that it may also be preparing to test-fire a long-range missile. Tensions have been running high since Kim Jong-Il's regime tested a nuclear bomb for the second time on May 25. It then launched a series of short-range missiles and renounced the truce that ended the Korean War in 1953. South Korean and US forces on the peninsula are on heightened alert after the North threatened a possible attack in response to Seoul's decision to join a US- led initiative to stop the spread of weapons of mass destruction. The North has warned of 'self-defence measures' in response to any tougher international sanctions, and US and South Korean officials have said it appears to be preparing to test-fire a long-range intercontinental ballistic missile. 