Under United Nations Security Council resolutions from 2006 and 2009, states, including China, are banned from helping North Korea with its ballistic missile programme, its nuclear activities as well as supplying heavy weapons.
Beijing has denied it has broken any rules, although a modern missile transporter seen in Sunday's military parade to celebrate the founder of North Korea was said by some western military experts to be of Chinese design and possibly origin.
"I'm sure there's been some help coming from China. I don't know, you know, the exact extent of that," Panetta told members of the House Armed Services Committee when asked whether China had been supporting North Korea's missile programme through "trade and technology exchanges".
North Korea's powerful Asian neighbour is Pyongyang's only major ally, with military and economic ties that date back to the communist origins of the two nations.
Pyongyang has said it was ready to retaliate in the face of widespread condemnation of the failed launch, increasing the likelihood the isolated state will go ahead with a third nuclear test. Late on Thursday it said it had "never recognised the UN Security Council resolution".
After last week's launch, which the United States said was a disguised long-range missile test but which Pyongyang insists was meant to put a satellite into orbit, the Obama administration said it had suspended a food aid deal.
Pyongyang retorted the food aid was "worth a petty amount of money".
China has called for "dialogue and communication" as tensions with North Korea mount and reiterated its long-standing call for a return to regional denuclearisation talks that have been stalled for years.