China's largest auto parts maker won U.S. government approval to buy A123 Systems, a maker of electric car batteries, despite warnings by some lawmakers that the deal would transfer sensitive technology developed with U.S. government money.

The sale of the lithium-ion battery maker to a U.S. unit of Wanxiang Group was approved by a U.S. government committee on foreign investment, according to a statement from the Chinese company. The companies later said the deal had been completed.

Last month, Wanxiang's U.S. unit agreed to pay $257 million for A123's automotive battery business and related assets in a bankruptcy auction, beating U.S. rival Johnson Controls of Milwaukee.

But the transaction still needed approval by the Committee on Foreign Investment in the United States, a government body led by the Treasury secretary. The committee approved the deal on Monday night, according to Wanxiang.

"Wanxiang America looks forward to closing the transaction and to continuing to foster the technologies A123 has worked so hard to develop," said Pin Ni, the president of Wanxiang America, in a statement.

Jason Forcier, president of the newly formed A123 Systems's auto business, said Wanxiang was focused on pushing A123 to profitability within a few years. "Wanxiang obviously brings financial stability to the company that we haven't had in at least the last six to 12 months," he said in a telephone interview.

Some members of Congress and the Strategic Materials Advisory Council -- a group including retired military leaders that is focused on protecting the U.S. industrial supply chain -- said the sale to Wanxiang could jeopardize U.S. energy security and they asked the U.S. committee to block it.

A123 had received a $249 million grant from the U.S. government as part of a stimulus program to promote clean energy, although about half of that money was never released.

The company filed for bankruptcy in October due to weaker-than-expected demand for hybrid vehicles and technical problems.

The company makes batteries for Fisker Automotive, BMW hybrid 3- and 5-Series cars, and General Motors's all-electric Chevrolet Spark, which is scheduled for release later this year. China's SAIC Motor and India's Tata Motors also are customers.

The money raised by the sale will be used to repay the battery maker's debts of about $376 million.

Wanxiang tried to blunt criticism of the deal by excluding A123's defense contracts from its bid at the auction. Those were sold separately to Illinois-based Navitas Systems for $2.25 million.

"There is no question that CFIUS process is there to fully protect national security issues and we are glad that we could have addressed all the concerns CFIUS has," Wanxiang America's president said in an email to Reuters.

Among the lawmakers who remained opposed to the sale were two senators who questioned the government's funding of the battery company even before its bankruptcy.

"Technology produced by A123 and funded by U.S. taxpayers should not simply be shipped off to China so that the military applications for these materials can be reproduced abroad," said a statement from Sen. John Thune, R-S.D.

Thune and Sen. Chuck Grassley, R-Iowa, called on CFIUS to give a full briefing on the A123 review.

A123 received its U.S. government funds, which it used to build manufacturing plants in Michigan, as part of a $90 billion program to promote clean energy.

Chinese companies have been pouring cash into overseas investments, and with that money has come concerns around the globe that companies with ties to Beijing may not play by free-market rules.

The CFIUS recently rejected a bid to build wind farms in Oregon by Ralls, owned by two executives of China's Sany Group. The committee has also blocked multiple deals by Huawei Technologies, a Chinese telecom equipment manufacturer.

Wanxiang may have soothed the concerns of CFIUS members with its history of investing in the United States.

The company generates about $1 billion in U.S. revenue by supplying parts to GM and Ford. It has bought or invested in more than 20 U.S. companies, many of which were in bankruptcy, according to a congressional report.

Forcier said with Wanxiang's backing, A123 will invest in areas where it sees growth, including batteries for hybrid and microhybrid vehicles. While the auto business will make up half of the company's sales this year, the electric grid unit is expected to become its largest business within the next several years.

He also said A123 hopes to leverage its ties to Wanxiang into more business in China, where it operates through a joint venture with SAIC. Forcier said A123 will operate as a stand-alone entity and no major job cuts are planned.