SEOUL (Reuters) - North Korea, defiant in the face of international condemnation of its latest nuclear test, fired two more short-range missiles off its east coast on Tuesday and accused the US of plotting against its government. In a move certain to compound tensions in the region, South Korea said it would join a US-led initiative to intercept ships suspected of carrying weapons of mass destruction, something Pyongyang has warned it would consider a declaration of war. South Koreas Yonhap news agency quoted a government source in Seoul as saying the North had test-fired one surface-to-air and one surface-to-ship missile off its east coast. The missiles had a range of about 130km. North Korea could also launch by Wednesday (today) more short-range missiles, perhaps towards a disputed sea border with the South, South Korean media quoted govt sources as saying. North Korea fired off three short-range missiles on Monday. Brushing aside international condemnation, Pyongyang said the United States was the aggressive one, its usual argument to justify having a nuclear arsenal. Our army and people are fully ready for battle ... against any reckless US attempt for a pre-emptive attack, the Norths KCNA news agency said. A North Korean diplomat told the 65-nation Geneva conference that denunciations of its nuclear test could prevent it from supporting the groups moves to curb production of nuclear bomb-making material, jeopardising the start of global talks on the issue. An Myung Hun said Mondays underground explosion was a self-defence measure. Interfax news agency in Moscow quoted a Russian Foreign Ministry source as saying the adoption of a tough resolution was probably unavoidable because the Security Councils authority was at stake.