The United Kingdom's second-most valuable listed company, pharmaceutical firm AstraZeneca, has been revealed to have been holding talks for some time with United States-based rival Bristol Myers Squibb, or BMS, about a merger, which could result in a global pharma giant worth nearly $400 billion.

The Financial Times reports that talks have been taking place for some months, although a deal is not yet thought to be close. If the merger between the British company, valued at $264 billion, and its US counterpart, worth around $133 billion, goes through, it would result in the global drug sector's fourth-largest company.

AstraZeneca declined to comment and BMS did not immediately respond to requests for comment, according to the FT.

Around the world, AstraZeneca generated $58.7 billion last year, and it has set itself a target revenue figure of $80 billion by 2030, which is why it is so keen to make further inroads into the US market, which already accounts for almost half of its revenue.

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