Since last August, search engine giant Google has been trying to buy struggling Motorola Mobility for $12.5 billion to complement its mobile software expertise. But, antitrust regulators around the world are delaying this deal by continuing to probe this multi-billion acquisition pact.

Although, the company had some luck last month in Europe when the EU regulators gave the deal a green signal, the Chinese antitrust regulators have extended their investigation into Google’s $12.5 billion purchase of Motorola Mobility. The two companies are calling it the last hurdle before it can be completed, reports Bloomberg.

In a regulatory filing on Monday, Libertyville, Ill.-based Motorola Mobility said, “China’s anti-monopoly bureau has expanded its second phase of the investigation,” wrote Bloomberg reporters Brian Womack and Hugo Miller.

Even though the two companies are expecting the transaction to close by the first half of the year, they cannot provide any assurance that it will be approved by China, wrote Womack and Miller.

According to the Bloomberg report, the Google-Motorola acquisition pact has been approved by regulators in Europe, the U.S. and some other countries around the world. Hence, as per the report, China looks like the last hurdle for this $12.5 billion purchase deal.

Facing legal battles over Android smartphone software, Google is counting on taking advantage of the 17,000 and more patents held by Motorola Mobility, wrote Womack and Miller. The data compiled by Bloomberg indicates that Google-Motorola deal is the largest in this decade.

Meanwhile, Mybroadband.com reports that upcoming Google-Motorola partnership has pushed Korean consumer giant Samsung towards BlackBerry maker Research In Motion (RIM). As a result, Samsung will use the BlackBerry 10 operating system (OS) developed by RIM in future Samsung smartphones, reported Mybroadband.