Google is making its vast online library of books available for mobile phones.

"We are excited to announce the launch of a mobile version of Google Book Search, opening up over 1.5 million mobile public domain books in the US (and over half a million outside the US) for you to browse," the company said.

The Internet search giant, in a post on Thursday on the Google Book Search blog, said mobile versions of the books could be read on devices such as the Apple iPhone or T-Mobile G1, which is powered by Google's Android software.

"These new mobile editions are optimized to be read on a small screen," Google said. "With this launch, we believe that we've taken an important step toward more universal access to books."

To access the mobile version of Google Book Search a user needs to type http://books.google.com/m into the Web browser of their iPhone or Android phone.

Google's announcement comes just days ahead of the expected unveiling by Amazon of a new generation version of its popular electronic book reader, the Kindle, at a New York press conference on Monday.

Amazon is also planning to make its online store of e-books for the Kindle available on mobile phones, the New York Times reported on Friday.

"We are excited to make Kindle books available on a range of mobile phones," Drew Herdener, an Amazon spokesman, told the Times. "We are working on that now."

The Amazon spokesman did not provide any further details.

Google will initially only be offering books in the public domain -- those which are not under copyright -- for mobile phones.

Amazon, on the other hand, offers the latest releases and 230,000 titles in all, including 103 of the 112 current New York Times bestsellers.