SAMSUNG Electronics said yesterday its latest flagship Galaxy S4 had become its fastest selling smartphone to date, topping 10 million units globally less than a month after its debut.

A company statement said the S4 had already passed the 10-million sales mark following its April 26 launch. It's predecessor, the S3, took 50 days to reach the same threshold.

The world's top handset maker hopes the S4 will expand its presence in high-end markets in the United States and elsewhere, crowding out archrival Apple and its iconic iPhone.

Apple has asked a US federal judge to add the S4 to the list of Samsung devices targeted in a patent lawsuit involving Siri personal assistant software.

"Apple's infringement theories regarding the S4 are identical to Apple's infringement theories against the already accused products," attorney Mark Lyon said in a motion filed on Tuesday on behalf of Apple.

The five patents at issue in the case include two associated with Siri voice-commanded personal assistant in iPhones.

The case is one of many legal battles between California-based Apple and Samsung.