FRANKFURT, Feb 13 (Reuters) - German drugmaker Boehringer Ingelheim said on Thursday it is facing more than 2,000 lawsuits in the United States over claims its blockbuster drug Pradaxa, the first in a new class of stroke prevention pills, caused severe and fatal bleeding.

The unlisted company confirmed the number of cases reported on Thursday by German newspaper Handelsblatt, adding the risk of side effects was known and had to be weighed against the drug's life saving potential.

"We are certain that we can show in the legal cases that we have worked very carefully and responsibly in research, development and marketing of Pradaxa," the company said in a written statement.

Pradaxa was the first to market in a promising new class of medicines designed to replace decades-old warfarin to prevent strokes in patients suffering from atrial fibrillation, a form of irregular heartbeat common among the elderly.

Like other blood thinners, Pradaxa's benefit of cutting the rate of fatal or debilitating strokes in the elderly comes at the risk of internal bleeding, which can also cost lives.

Boehringer cited a recent study by the U.S. Food and Drug Administration as showing that Pradaxa users ran a lower risk of severe bleedings than patients on warfarin.

Sales of the pill - which competes with Bayer and Johnson & Johnson's Xarelto as well as Bristol Myers-Squibb and Pfizer's Eliquis - were 1.1 billion euros ($1.5 billion) in 2012, its second year of market approval.