SAN FRANCISCO (Reuters) - Apple Inc is working on a cheaper version of its popular iPhone that could be released this year, according to a report in the Wall Street Journal on Tuesday.

The device could resemble the existing iPhone, but might use less expensive materials, such as a shell made of polycarbonate plastic, according to the report, which cited anonymous sources.

Apple could decide not to move forward with the lower-end iPhone, the report noted.

The product would represent the first time Apple has diversified its line of smartphones with significantly different models since launching the original iPhone in 2007. The company faces pressure from rival smartphone-makers such as Samsung Electronics Co LTD whose products use Google Inc's Android operating system.

Apple declined to comment on the report.

Shares of Apple, which closed Tuesday's regular trading session at $525.31, are down 25.5 percent from their 52-week high of $705.07 in September.

(Reporting By Alexei Oreskovic; Editing by David Gregorio)