A U.S. trade judge has hinted that Apple may struggle to invalidate patents owned by HTC, which could potentially lead to an import ban on the latest iPad and the forthcoming iPhone.

According to Bloomberg, U.S. International Trade Commission (ITC) Judge Thomas Pender said in Washington on Thursday that "clear and convincing means something to me," speaking about the legalities of determining whether a patent should or shouldn't have been issued.

"I have to be pretty darn certain a U.S. patent is invalid," Pender added.

HTC accused Apple of infringing two patents relating to 4G technologies. While the current iPad (aka the iPad 3) already boasts 4G connectivity -- available only in North America, which led to Apple being chastised by U.K. and Australian regulators for dubbing the device as "4G" when it could not connect to local networks in their regions -- the forthcoming iPhone is thought to include the next-generation network standard. Apple is widely expected to announce the iPhone 5 at a press event this Wednesday.

If Apple is found to have infringed HTC's patents, that could lead to a U.S. import ban on the iPad and iPhone 5, or give HTC enough ammunition to push for a settlement with Apple, which has its own patent claims filed against the Taiwanese smartphone maker.

The two companies have been locked in legal tussles for the last three years. After Apple sued HTC over iPhone patents in March 2010, the ITC's initial ruling came down in Apple's favor, stating that HTC had violated two of Apple's patents.

In 2011, HTC fired off its own patent lawsuit against the iPhone and iPad maker over Wi-Fi-related patents. HTC sought an import ban of Apple's line of Macs, iPads, iPods, iPhones, and other Wi-Fi enabled devices.

Earlier this year, HTC scored a victory over Apple at the U.K. High Court, after a judge ruled that three of the four Apple-owned patents in Europe were invalid. HTC was not found to have infringed the fourth patent, which related to photo management software.

While HTC is not the healthiest of companies in the smartphone space, the firm still holds a 6 percent stake in the U.S. smartphone market; partially thanks to Research in Motion's dwindling down the top five smartphone makers, as the BlackBerry maker continues its struggle for relevance and market share in an already burgeoning smartphone sector.