Seoul: US President Barack Obama said on Sunday it was unclear who was "calling the shots" in North Korea under its untested new leader and stepped up demands for Pyongyang to abort its planned rocket launch.

Obama stood with South Korean President Lee Myung-Bak to present a united front against the communist North, hours after staring into what he termed a "time warp" as he visited the last land border left over from the Cold War.
The US leader also had some unusually public criticism of China for its failure to induce its North Korean ally to open its nuclear programme to inspections and to end years of "provocations" and "bad behaviour".
His comments in Seoul also deepened speculation about the elevation of new North Korean leader Kim Jong-Un, and raised the alarming prospect of a power struggle in a volatile and erratic nation armed with nuclear weapons.
Obama told reporters it was "hard to have an impression" of the young leader who took over after his father Kim Jong-Il died from a heart attack in December.
"The situation in North Korea appears unsettled. It is not clear exactly who is calling the shots and what their long-term objectives are," Obama said in Washington's frankest assessment yet of Pyongyang's murky power politics.
The president got an up-close look into the isolated Stalinist state when he climbed a clifftop observation post 25 metres from the demarcation line that has divided the Koreas for six decades.
After squinting through high-powered binoculars from behind a bulletproof screen over a border guarded by mines, barbed wire and tank traps, Obama said he had stared into a "time warp".
He then turned towards a huge North Korean flag flapping in the stiff breeze at half-mast to mark the 100th day since Kim Jong-Il's death, and at a horizon dotted with rudimentary buildings peeking through the haze.
The visit, during which Obama told some of the 28,500 US troops guarding South Korea that they stood at "freedom's frontier", was meant as a firm show of unity with Seoul and appeared partly aimed at Kim Jong-Un.