Bratton said Friday there is "no specific credible threat" to New York City.
He says the NYPD is working with the FBI Joint Terrorism Task Force to monitor any developments.
The commissioner added that New York City's "security posture" and NYPD resources are adjusted daily to conform to changing conditions around the globe.
Britain's decision was related to developments in Iraq and Syria, but there was no information to suggest an attack was imminent.
Prime Minister David Cameron told reporters that while the Taliban facilitated al-Qaida terrorism, the Islamic State group is "effectively a state run by terrorists.""We could be facing a terrorist state on the shores of the Mediterranean and bordering a NATO member," he said.
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