Pharmaceuticals maker Pfizer Inc announced Monday its purchase of competitor Wyeth in a deal worth 68 billion dollars, the companies announced in a joint statement.

It would be one of the biggest takeovers in years and the most important one since the outbreak of the financial crisis. The last deal of comparable size was the AT&T-BellSouth merger for 70 billion dollars in March 2006.

"Our employees should be enormously proud of what we have built and confident that combining with Pfizer will accelerate our pursuit of innovative new medicines to meet critical unmet patient needs," said Bernard Poussot, chairman, president and chief executive officer at Wyeth.

"Wyeth and Pfizer are highly complementary businesses, and together we can build the best diversified health care company in the world."

Pfizer will pay for the takeover with a mixture of cash and shares. Additionally, a consortium of banks has promised to lend about 22.5 billion dollars to pave the way for the merger.

Combined, the two companies have sales of around 75 billion dollars.

A statement said the companies expect to cut costs in sales, administration, research and development and manufacturing thanks to the merger.

The companies also expect to be able to diversify their offerings with the merger, with no single drug accounting for more than 10 per cent of the joint venture's profits in 2012.

Pfizer took over competitor Pharmacia in 2003 for 64 billion dollars, the last major mergers in the sector.