AstraZeneca's chief executive Pascal Soriot said in an interview with the news agency Reuters 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.

Soriot stressed that 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," the French national, CEO at AstraZeneca since 2013, said.

"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," he added.

Pfizer's cash-and-stock takeover approach on May 2 values AstraZeneca at $106 billion. The bid was promptly dismissed by the British group's board, a decision Soriot said had the firm backing of investors.

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

In particular, he highlighted 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.

Soriot said 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 redomicile in Britain in order to minimise 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," the UK drugmaker's chief said.