The US patent office has rejected two more of the NTP patents involved in the company's lawsuit against Research In Motion (RIM), which may lead to a shutdown of BlackBerry service in the US.

However NTP has also been granted a 30-day extension by the USPTO to give it more time to file a defence of patents rejected earlier.

RIM said on Friday that the patent office had issued "non-final actions" rejecting two of NTP's patent claims. "The Patent Office's latest rulings corroborate RIM's long-standing contention that the NTP patents are invalid," said Mark Guibert, RIM's vice president of corporate marketing, in a statement.

Patents going through a re-examination process are regularly rejected, but it is far less likely for patents to be rejected in the ensuing appeals process. For example, the notorious Web browser patent owned by Eolas was rejected by the patent office in the two initial stages of re-examination, only to be found valid in September of 2005.

NTP has said it will press on with the full appeals process through the US PTO, which could take until the end of 2006.

Last week, NTP said it had been granted a 30-day extension in the process of defending patents rejected earlier on by the patent office, but claimed the extension wouldn't delay re-examination.

NTP said it needed the extra time in order to allow one of its experts to help draft the response, according to reports.

The patent office recently said it would fast-track re-examination because of the NTP-RIM court fracas. So far the office has rejected seven of the eight NTP patents involved in the case.

RIM could be vindicated if the US patent office ultimately rejects NTP's patents. However, a more pressing deadline could arrive as soon as February, when US District Court Judge James Spencer is scheduled to consider imposing a ban on BlackBerry sales and e-mail service in the US.

NTP successfully sued RIM for patent infringement in 2002 and won an injunction, which was stayed pending appeal. The appeals process is now largely exhausted, moving RIM closer to a possible shutdown.