A supreme court decision on abortion widely seen as the most important legal victory for the religious right in years has opened up a rift within the anti-abortion movement. In a full-page advertisement in a Colorado newspaper yesterday, the leaders of four anti-abortion groups accused a powerful evangelical leader of misleading his fellow Christians on the court verdict. The unusual attack on James Dobson, the founder of Focus on Family and arguably one of the most powerful figures on the religious right, comes only days after the death of the Rev Jerry Falwell, a leading conservative.

The breach prompted immediate speculation about cracks in what has until now been a remarkably united movement.

In their ad, the leaders of the four anti-abortion groups say Mr Dobson was wrong to see last April's supreme court decision as a victory. The verdict banned a particular procedure for terminations later in pregnancy, which the anti-abortion movement has labeled "partial birth abortions".

The campaign against that particular procedure has been a rallying point in the anti-abortion movement. Last month's decision was also seen as an indication of a shift to the right on the supreme court following two appointments by President Bush. Opponents of abortion now believe it could soon be possible to overturn the decision legalizing abortion.

However, yesterday's ad argues that the ban on late abortions will not reduce terminations. Instead, the ad says the ban will simply encourage doctors to find other methods for such terminations.

"Dr Dobson, you mislead Christians claiming this ruling will 'protect children.' The court granted no authority to save the life of even a single child," the ad said. It also called on Mr Dobson to repent.