Sources: U.S. drone strike kills at least 50 in Yemen

This comes as the United States and the Yemeni government step up their efforts to target militants, including those Islamists who've taken over several cities in recent weeks.

The government claims that a U.S. drone was not involved in the attack and that its air forces conducted the raid. The interior ministry said on its website that nine fighters were killed, but dozens were injured and that the number of deaths is expected to rise.

There was no immediate comment from U.S. officials.

Both sources, a security official and a senior security source, didn't want their names used because they are not authorized to speak to the media.

The airstrike occurred in al-Wathee district in Abyan province. One of the sources said more than a dozen people were injured.

The strike targeted a police station which had been taken over by suspected al Qaeda fighters, the sources said. U.S. drones have been seen flying over the area every day and more attacks are expected, the sources told CNN.

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