Ren Jianxin (center), chairman of China National Chemical Corp, listens while Michel Demare, president of Swiss agrochemicals maker Syngenta AG, addresses the annual news conference as at the company's headquarters in Basel, Switzerland, in February. [Photo/Agencies]

China National Chemical Corp is seeking more time for the United States to complete a national security review of its planned takeover of Swiss chemical company Syngenta AG, according to people familiar with the matter.

The companies resubmitted the $43 billion transaction to the government panel that reviews acquisitions of US businesses by foreign investors, said the people, who asked not to be named because the process is confidential.

The Committee on Foreign Investment in the US, which can recommend to the president that transactions be blocked if they allegedly pose a risk to national security, has a maximum of 75 days to complete reviews. Refiling restarts that clock.

Syngenta, which got more than a quarter of its revenue last year from seeds and crop protection in North America, would help transform State-owned ChemChina into the world's biggest supplier of pesticides and agrochemicals. The bid comes amid a record wave of Chinese investment that has prompted US officials to consider claims that some of the acquisitions could threaten national security.

"A withdrawal and refiling likely mean that there are ongoing mitigation discussions, or that CFIUS needs more time to do its due diligence," said Anne Salladin, an attorney at Stroock & Stroock & Lavan LLP in Washington, who is not involved in the transaction.

"While the CFIUS process is not inherently political, the implication of a more high-profile deal can often be a more rigorous review and investigation that takes more time."

The companies haven't said whether they hit resistance from the panel over possible security risks or need more time to negotiate changes to the deal to resolve any concerns.

ChemChina and Syngenta also haven't divulged when they refiled with the committee, which could also clear the deal without changes.

Investigations by CFIUS, which is led by the US Treasury Department and includes officials from the Defense, State and Homeland Security departments, are confidential. The panel doesn't comment on active reviews.

Representatives for ChemChina and Syngenta declined to comment.