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The US has boosted its security presence and tactics in Washington and New York amid fears of a "credible terror threat" meant to coincide with the 10th anniversary of the September 11, 2001, attacks.

The increased security came as Ray Kelly, head of the New York Police Department, has been accused by civil rights groups of over-stepping the department's jurisdiction by using its ties with intelligence services to illegally obtain information.

Among the tactics that critics find controversial, the NYPD has sent undercover officers into predominantly Muslim areas to monitor communities, including listening to sermons at mosques.

Speaking to Al Jazeera, Kelly denied the claims, saying his department's intelligence gathering was only used to protect the public.

Al Jazeera correspondent Scott Heidler reports from New York.

Source: Al Jazeera