A Jordanian man stabbed his sister to death with a dagger in an "honor killing" because of rumors she was dating a man, a police official said Thursday.

The 24-year-old farmer, who turned himself in and confessed to the killing, was charged with murder, the official said.

An autopsy showed the victim, who was 27 years old, was four weeks pregnant, he said, speaking on condition of anonymity because he was not authorized to speak to journalists.

The man said in his confession that he killed his sister because he heard rumors she was dating a man, the official said.

In some conservative areas of Jordan and elsewhere in the Middle East, people disapprove of an unwed woman having any relationship with an unrelated man and consider it to reflect negatively on her family.

An average of 20 Jordanian women are killed annually in slayings that are known as honor killings because the perpetrators say they believe their actions will restore their family's community standing.

The government has battled the problem with harsher sentences for perpetrators.