The hermit nation has been spotted digging tunnels at a SECRET nuclear test site, in the northeastern tip of the country. Its military has conducted three nuclear tests in tunnels at Punggye-ri – in 2006, 2009 and 2013. South Korean believe its volatile neighbour is preparing for a FOURTH show of strength. The alarming new development comes just weeks after leader Kim Jong-un warned the US he was "ready for WAR". [caption id="attachment_42811" align="aligncenter" width="620"]TEST SITE: The Punggye - ri test site pictured earlier this year[/ caption] An official told the Yonhap news agency: " An increased movement of people and cars has been spotted at the nuclear site. " North Korea appears to be in the process of digging another tunnel. " Another source said that the movement indicated the North was preparing to test another thermonuclear weapon – bit more analysis was needed to determine if the blast was imminent.[caption id = " attachment _ 42812 " align = " aligncenter " width = " 620 "]SUPREME LEADER: Jong - un is the third in the Kim dynasty started by his grandfather[/ caption] The sighting comes after the paranoid North showed off its atomic arsenal and hinted it may test another nuke in response to the West ' s " hostile ".Recommended:N. Korea gets ready for warA huge parade to mark the 70th anniversary of North Korea ' s ruling Workers Party featured KN - 08 intercontinental ballistic missiles – which some analysts believe can reach the US. Korean state television boasted the missiles – fitted with nuclear warheads – could destroy its enemies in a " sea of fire ". The chubby dictator bragged: " Our revolutionary force is ready to respond to any kind of war the American imperialists want. " Through the line of ' military - first ' politics, our Korean People ' s Army has become the strongest revolutionary force and our country has become an impenetrable fortress and a global military power. "[caption id = " attachment _ 42813 " align = " aligncenter " width = " 620 "]PRIMED: The KN - 08 – said to be armed with nuclear warheads[/ caption] The Communist regime has long claimed to possess sophisticated nuclear weapons and KN - 08 missiles have been seen before.Recommended:70th anniversary parade in North Korea[Video]But the missile tips were a different shape – and the state claimed they were are armed with nuclear warheads. The television commentator threatened: “With the vengeful desire to turn the citadel of our enemies into a sea of fire, our powerful tactical rockets loaded with diversified and miniaturised nuclear warheads are on the move. ”[caption id = " attachment _ 42814 " align = " aligncenter " width = " 620 "]TANKED UP: Tanks, armoured vehicles and rocket launchers featured in the parade[/ caption] Lee Il - Woo – a defence analyst at Korea Defence Network – said the new version of the KN - 08 – which can fly 7,500 miles – had a more rounded end than the version unveiled in 2012. “This means North Korea might have successfully developed technology to minimise nuclear warheads and fit them on top of missiles, ” he said. The West is facing a barrage of atomic threats from across hostile nations. A Chinese official said war with the US was " inevitable " after the countries clashed over a set of disputed islands. The country unveiled a " scattergun " rocket capable of firing 20 nuclear warheads earlier this month. North Korea may also be trying to strengthen its bargaining hand ahead of a key pow wow with South Korea, China and Japan planned for Sunday.This article originally appeared on Daily Star