U.K. pharmaceutical giant AstraZeneca is considering a deal to merge with its U.S. competitor Bristol Myers Squibb, in a deal that would value the joint company at roughly $400 billion, the Financial Times reported on Sunday.

It's still unclear whether the deal will come together, but the companies have been discussing a merger over the last few months, sources told the FT.

The merger would be one of the largest in history.

AstraZeneca and Bristol Myers Squibb did not immediately respond to a CNBC request for comment.

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