LONDON -- British police say 22 people have been arrested outside of the U.S. Embassy in London during a protest over the American use of drones in Pakistan.

Scotland Yard confirmed the arrests Friday at the demonstration, organized by a group calling itself "United Ummah."

Police said 20 people were arrested on suspicion of being members of a group banned by the Home Office. It would not say what group it believed the suspects belong to. One other person was arrested for violent disorder and another for obstruction.

"United Ummah" does not appear on the Home Office's list of banned groups, but prescribed organizations have rebranded themselves in the past after they were featured.

The demonstration was advertised online -- on YouTube, Twitter and various forums -- and in a publicity video as a gathering to expose "the recent spate of anti-Muslim drone strikes that have been launched by the U.S. government against innocent Muslims."

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U.S. and Pakistan diplomatic relations hit a new low following U.S.-led NATO strikes that killed 24 Pakistani soldiers last week, with officials from both countries offering different accounts of how two Pakistan army posts were attacked before dawn Saturday.

According to U.S. military records described to The Associated Press, the incident occurred when a joint U.S. and Afghan patrol requested backup after being attacked by Taliban militants.

Before responding, the patrol first checked with the Pakistani army, which reported it had no troops in the area, the account said.

Pakistani officials have refuted this claim and said U.S. forces must have known they were attacking Pakistani soldiers because the posts were clearly marked on maps given to NATO and the two sides were in contact immediately before and during the airstrikes.