The Android operating system (OS) is coming under pressure in the US smartphone market, with new figures from Strategy Analytics claiming that the platform lost ground to major rival Apple iOS in the last quarter.

“We estimate Android shipped 13.4 million smartphones for 56 percent share of the United States market in the second quarter of 2012. This was down from 15.3 million units shipped and 61 percent share a year earlier,” noted Neil Mawston, Executive Director at Strategy Analytics, in a statement. Mawston added that although Android remains the number one platform by volume in the US, its market share is approaching a peak and Apple iOS has been gaining ground. Indeed, Apple’s US market share has risen by ten points from 23 percent in Q2 2011 to 33 percent in Q2 2012.

The numbers will alarm Android’s backers, especially since Apple’s most recent quarter was generally perceived to have been slightly weak for the Cupertino-based vendor (at least by Apple’s very high standards). “Apple is rumored to be launching a new iPhone in the coming weeks, and that event, if it takes place, is going to heap even more pressure on Android in its home market,” added Mawston.

Elsewhere in Strategy Analytics’ numbers, RIM’s recent woes led to an unsurprising fall in market share for BlackBerry OS (6.5 percent in Q2 2012 compared to 10.5 percent a year ago), while the ‘Others’ category also experienced a drop (from 5.7 percent market share to 4 percent). Microsoft’s Windows Phone OS is believed to make up a significant proportion of this ‘Others’ category, suggesting the Nokia/Microsoft smartphone alliance continues to struggle in the US.

Total shipments of US smartphones in Q2 2012 fell 5 percent annually to reach 24 million units, representing one of the slowest growth rates ever experienced in the country. “A volatile economy, maturing penetration of smartphones among contract mobile subscribers, and major operators tightening their upgrade policies to enhance profits were among the main causes of the slowdown,” commented Alex Spektor, Associate Director at Strategy Analytics.