North Korea is upgrading jamming devices to disrupt South Korean military communications, Yonhap news agency said Tuesday, citing a defence ministry report.

The communist state has some 20 types of jamming devices mostly imported from Russia and it has been developing a new device with a range of more than 100 kilometres (60 miles), the South Korean news agency said.

Yonhap cited a defence ministry report to the parliamentary defence committee. The ministry declined to comment, saying the report was confidential.

North Korea is known to have deployed jamming devices to the heavily-fortified border that are capable of disrupting Global Positioning System (GPS) signals within 50 to 100 kilometres, it said.

The North is thought to have been responsible for the intermittent failure of GPS receivers on naval and civilian craft along the west coast in August 2010.

South Korea's then-defence minister Kim Tae-Young said at the time that the devices could disrupt guided weapons and posed "a fresh security threat" to Seoul.

Seoul mobile users also complained of bad connections and the military reported GPS navigational devices malfunctioning in March, while the South and the US were staging a joint military drill criticised by the North.

The UN's International Telecommunication Union in April urged the North to stop disrupting signals in the South.

Yonhap also cited the report as saying the North could soon begin developing electromagnetic pulse (EMP) bombs that could paralyse communications via electronic signals.

"We don't have any confirmed intelligence, but given the rate of the North's development of new electronic devices and EMP development in other nations, it's possible that the North will also develop (EMP bombs)," it cited the report as saying.