The European Patent Office said Wednesday it had added restrictions to a controversial patent granted in 1999 so that it could not be used to clone humans, a ruling limiting biotech research in Europe.

The Munich-based office said it had revised the patent it granted to Edinburgh University, Scotland, in December 1999 on altering animal cells after objections from 14 parties.

The patent office said officials had not noticed a reference to human cells in the original 235-page application document.