Apple recently threatened retailers in a Singapore mall with legal action if they continue to sell unlocked iPhones, prompting many to stop selling the handsets, The Straits Times newspaper reported on Friday.

"Apple threatened in an email to go after them for illegally 'unlocking' parallel imported iPhones," the newspaper reported on Friday, citing several anonymous sources. Apple threatened to pursue damages of S$1,000 for every unlocked iPhone sold by retailers in Sim Lim Square, a local mall full of electronics shops, the report said.

The Straits Times report indicated Apple's threats rest on a claim that unlocking the iPhone was a violation of the software licence agreement. That is not the case in the US, where laws provide a specific exemption that allows users to unlock mobile phones.

Apple was not available to comment on the report.

The iPhone is not officially available in Singapore, but unlocked handsets have been on sale for some time in local electronics markets, as they have in other countries around Asia. However, calls to several shops in Sim Lim Square on Friday confirmed that unlocked iPhones have become scarce.

"We used to sell it, but not anymore," said a sales manager at Royal Plus Pacific, an electronics shop in Sim Lim Square. The shop stopped selling iPhones because they ran out of stock, he said, adding they hadn't received a threatening email from Apple.