AstraZeneca shareholder Schroders has urged the pharmaceutical firm to reconsider its rejection of a takeover offer from U.S. drugmaker Pfizer.

The fund manager, which holds a 2 percent stake in AstraZeneca, is the biggest shareholder to call publicly for renewed takeover talks.

Schroders said Tuesday it "notes with disappointment the quick rejection by the AstraZeneca board of the latest offer from Pfizer." It urged AstraZeneca management "to recommence their engagement with Pfizer, and subsequently their shareholders."

The board of AstraZeneca this week rejected an improved $119 billion takeover offer from Pfizer, saying it significantly undervalued the company and its drug portfolio.

Under British takeover rules Pfizer has until Monday to submit a new offer, but it has said it won't raise its offer again or launch a hostile takeover bid.