Samsung extended its lead over Apple in the smartphone market in the second quarter despite a slowing demand for mobile phones, according to figures released Tuesday.

Samsung sold 90.4 million mobile phones during the quarter, an increase of 29.5 percent compared to the same three-month period a year earlier, according to market-tracker Gartner Research.

Smartphones accounted for slightly more than half of the South Korean firm's handset sales, with people snapping up Samsung Galaxy smartphones powered by Google-backed Android software, Gartner reported.

Demand for the Galaxy S3 model topped Samsung's expectations, with 10 million reportedly being sold in the two months after its May release in a buying onslaught that caused product shortages.

Apple sold 28.9 million iPhones to claim 6.9 percent of the mobile handset market while Samsung's share climbed to 21.6 percent.

Meanwhile, worldwide mobile phones sales were said to have slipped 2.3 percent to 419 million units from the total seen in last year's second quarter.

"Demand slowed further in the second quarter of 2012," said Gartner principal research analyst Anshul Gupta.

"The challenging economic environment and users postponing upgrades to take advantage of high-profile device launches and promotions available later in the year slowed demand across markets."

Apple is expected to unveil a new iPhone model in September prompting rivals to either discount or upgrade product lines in response.

Sales of feature phones, handsets that do not boast the computing versatility of smartphones, continued to decline in the quarter weakening the overall mobile phone market, Gupta said.

Smartphones accounted for 36.7 percent of handset sales in a growing portion of the market, Gartner reported.

Gupta predicted that high-profile smartphone launches such as an Apple iPhone 5, along with device launches from Chinese manufacturers in the remaining months of this year, will fuel demand.

"Samsung and Apple continued to dominate the smartphone market, together taking about half the market share, and widening the gap to other manufacturers," Gupta said.

Nokia was the second-place mobile phone seller but its share of the market declined 14.8 percent as it relied heavily on feature phone sales while trying to gain traction with Lumia smartphones, according to Gartner.