(Reuters) -- Syngenta AG rejected ChemChina's offer to buy the Swiss agricultural chemicals group in a deal valued at about $42 billion, citing regulatory concerns, Bloomberg reported on Thursday.

China National Chemical Corp, better known as ChemChina, offered about 449 Swiss francs per share for Syngenta, valuing the Basel, Switzerland, company at about 41.7 billion Swiss francs ($41.72 billion), according to the report.

The offer follows a similarly priced bid from Monsanto Co that was withdrawn after Syngenta dismissed it as too low.

The two companies are still in talks and an agreement could still be reached in the next few weeks, Bloomberg said, citing sources.

Syngenta is also talking to other potential suitors, the news agency said.

U.S.-listed shares of Syngenta were up 14 percent at $79.22 in extended trading on Thursday.

Syngenta and ChemChina could not immediately be reached for comments.

(Reporting by Ismail Shakil in Bengaluru; Editing by Anil D'Silva)