WASHINGTON (AFP) - China's investment in the United States (US) doubled to US$14 billion (S$17.7 billion) last year despite sometimes rocky political ties, with private firms leading the way, said a study out on Tuesday.

About half of the value consisted of Shuanghui International's takeover of prominent pork producer Smithfield Foods, a US$7.1 billion deal that marked the largest ever Chinese acquisition of a US company.

But the report by the Rhodium Group, a New York-based firm that looks closely at Chinese investment, found that the total number of deals had also risen from 2012 to 82. It said that Chinese companies accounted for 70,000 full-time jobs in the United States.

The total value of investment hit a record high of US$14 billion, with high-profile deals in real estate as well as Chinese investors took stakes in the General Motors Building and Chase Manhattan Plaza in New York.

Private firms and entrepreneurs dominated, accounting for 87 per cent of transactions and 76 per cent of the total value of Chinese investment, a contrast to the dominance of state firms until recently, the study said.

US lawmakers have raised concern about investments by several Chinese firms. Telecoms giant Huawei has largely dropped hopes of expansion in the world's largest economy after Congress warned that its equipment could be used for spying.

The US has also raised intellectual property as a top concern with China, accusing hackers in the emerging economy of waging a vast theft campaign of American companies' trade secrets.

But the Rhodium Group said that most deals that failed were not linked to politics. It predicted future growth in investment.

"With its large market, educated workforce and world-leading technology and brands, the US has strong appeal to the next generation of Chinese outbound investors," it said.