SEOUL (AFP) - North Korea threatened Tuesday to bolster its "nuclear armed force," saying the United States was not yet ready to drop its "hostile policy" towards the communist country. Washington and Pyongyang face "a grave political challenge" to realise denuclearisation of the Korean peninsula and end their decades-long hostility, the North's state newspaper Minju Joson said in a commentary. "What is crucial here is that the US should completely abandon its hostile policy. But the US is not yet prepared to make a strategic decision," the commentary said. "As we have stressed several times, our nuclear armed force is a self-defensive measure to protect the security of our country and people against manoeuvres by hostile forces to stifle the DPRK (North Korea)," it said. "Therefore, the stronger US military threats and schemes to invade us are, the more our republic will keep strengthening its powerful self-defensive deterrence. That is our right." Pyongyang - which tested a nuclear weapon in October 2006 - handed over a partial accounting of its plutonium-related programmes to China in early July as part of six-nation talks to disarm the North. Washington is party to those talks. The North has also agreed to finish disabling its main plants by the end of October and to allow thorough verification by the parties. As part of the deal, the other five parties have guaranteed delivery of all heavy fuel oil promised as part of energy aid by the end of October. After Pyongyang handed over the declaration, Washington eased economic sanctions on the isolated country and initiated the process to remove North Korea from a blacklist of countries that allegedly sponsor terrorism. But North Korean Foreign Minister Pak Ui-Chun said at a security forum in Singapore last week that Washington had not lived up to its part of the deal. The six-nation talks - which also include South Korea, Japan and Russia - began in 2003. The North's state media has often issued similar commentaries urging Washington to take quick action in dropping Pyongyang from a list of state sponsors of terrorism.