The report came as North Korea stepped up its war rhetoric against the U.S. and South Korea after the allies started their annual drills aimed at improving their defense capabilities.

The North's People's Army recently launched a division supervising operational deployment of missiles with a range of more than 3,000km (1,860 miles) that it had developed in recent years, Yonhap news agency reported citing an unidentified South Korean government source. The missiles could pose a threat to U.S. forces in Japan, Guam and other Pacific areas that are to be redeployed in time of emergency on the Korean peninsula, Yonhap said.

The report, however, didn't provide further details such as how many missiles the new division possesses and where they are positioned.

South Korea's Defense Ministry said yesterday it couldn't confirm the Yonhap report. However, a ministry document published last year showed that the North deployed a new type of medium-range missile believed to be the same as one it displayed during a military parade in 2007.

If confirmed, the division's launch could suggest that the North has succeeded in developing more medium-range missiles since 2007 and it needed a bigger unit to manage them, said Ohm Tae-am of the state-run Korea Institute for Defense Analyses in Seoul.

The division's creation would also mean the North has a unit whose primary role is to prevent the U.S. from redeploying its troops in the Pacific to the Korean peninsula in the event of a conflict, said Baek Seung-joo of the same institute.

North Korea's missile program and nuclear weapons development program are major regional security concerns.

The North conducted a long-range rocket test in April in violation of a U.N. Security Council resolution that prohibits the country from engaging in any ballistic missile-related activities. A defiant Pyongyang subsequently quit nuclear disarmament talks and performed a second nuclear test.

The United Nations responded in July by imposing punishing new sanctions that toughened an arms embargo on the country and authorized ship searches on the high seas. Yesterday, the North continued its salvo against the U.S. and South Korea over their military drills, which the regime has long slammed as a rehearsal for invasion.

"This cannot be interpreted otherwise than a grave provocation," the North's Foreign Ministry said in a statement. It said the North will continue to bolster its nuclear capability as long as the U.S. military threats persist.