The chief executive of Amgen said Monday that the company’s decision to sell Japanese distribution rights to many of the drugs in its pipeline was not solely a response to financial pressures caused by the decline in sales of Amgen’s flagship anemia drugs, the New York Times rerpots.

Kevin W. Sharer, the chief executive, said the deal, which was announced early Monday and could bring the company as much as $1.2 billion, was forged because Amgen had too many experimental compounds to develop on its own.

“We just can’t, either operationally or financially, develop all these molecules in the three principal geographies,” he said, referring to the United States, Europe and Japan. He said financial pressures contributed to the timing of the deal. But “this was an inevitable development” because of the high costs of research and development, he said.

The pact calls for Amgen to sell Japanese rights to up to 13 of its experimental drugs to the Takeda Pharmaceutical Company, Japan’s largest drug company.

Takeda will pay Amgen $200 million upfront. It will also chip in up to $340 million to help develop the drugs worldwide over the next several years, helping to defray Amgen’s costs of testing the drugs for use in the United States and Europe.

It will also pay up to $362 million more if certain milestones are achieved in development, plus royalties on sales of the drugs in Japan. Takeda is also buying Amgen’s Japanese subsidiary, Amgen KK.