AstraZeneca's boss said on Wednesday he would engage with Pfizer if the price was right and the risks posed from forcing the British drugmaker's operations into the U.S. company's new three-unit model were addressed.

Chief Executive Pascal Soriot stressed his company had a bright future as a stand-alone firm but acknowledged that shareholders would expect AstraZeneca's board to negotiate if terms were sufficiently attractive in a sweetened offer.

"Every shareholder says at the right level with the right offer you should consider it - that is very clear. But there is nobody who has told us a specific price at which we should engage," he told Reuters in an interview.

"If the offer was reflecting the value of the company but also addressing some of the integration aspects, the operating model and execution risks we are concerned about, then we certainly should engage - there's no doubt."

Pfizer made a cash-and-stock takeover approach on May 2 worth 50 pounds a share to create the world's largest drugs company, valuing AstraZeneca at $106 billion. The bid was promptly dismissed by the British group's board - a decision that Soriot said had the firm backing of investors.

"There is no single shareholder who has told me or our CFO (chief financial officer) or our chairman that we should have accepted the offer," he said.

Soriot has already set out his case for an independent future for AstraZeneca, based on a promising pipeline of new drugs, but has left the door ajar to a compelling offer.

In addition to price and the share of cash in any sweetened offer, Soriot said AstraZeneca would also need assurances about the risks faced by Pfizer in implementing a complex merger and integrating operations across two sprawling organizations.

In particular, he highlighted the problems posed by the fact

that Pfizer is now separating its operations into three business units - a structure that would clash with AstraZeneca, where the MedImmune biotech unit, for example, serves all parts the group.

He is also worried about diluting the focus on science in the new group and the risk to reputation in Pfizer's controversial plan to re-domicile in Britain in order to minimize its tax payments.

"All those issues will need to be discussed, but step one is to get to an offer that reflects the value of the company," Soriot said.

(Reporting by Ben Hirschler. Editing by Jane Merriman)