Pfizer Inc, the world's biggest drugmaker, will close six research and development sites and trim jobs in the Unites States and the United Kingdom, following the acquisition of Wyeth.

The company on Monday said it will reduce its global research and development square footage by 35%.

Pfizer will discontinue R&D operations in Princeton, New Jersey; Chazy, Rouses Point and Plattsburgh, New York; Sanford and Research Triangle Park, North Carolina; and Gosport, Slough/Taplow, United Kingdom.

"While these changes are expected to bolster productivity and reduce costs, they will result in staff reductions," Pfizer said in a statement.

Pfizer will now conduct R&D at five main sites and nine specialized units around the world, as compared with 20 sites upon closing the acquisition of Wyeth.

The company did not elaborate on the number of jobs that will be cut. A spokeswoman could not be immediately reached for comment.

Pfizer, already the world's largest drugmaker, got much bigger last month with completion of a USD 67.3 billion acquisition of Wyeth.