The U.S. Embassy in Moscow said on Friday it was monitoring reports of "imminent" extremist plans to target large gatherings in the Russian capital over the over the next 48 hours.

The big picture: The embassy did not disclose any other information about the reported threats but warned U.S. citizens to avoid crowds and to be aware of their surroundings.

Zoom in: The embassy issued its warning hours after Russia's Federal Security Service (FSB), the successor to the Soviet-era KGB, said it thwarted an attack on a synagogue by an Islamic State cell, Reuters reports.

• Though it's unclear if the two statements are related, the FSB said the cell was planning on attacking "the congregants of a synagogue using firearms."
• After the attack was foiled, it said it found and seized firearms, ammunition and components for manufacturing an improvised explosive device.

Zoom out: Since the beginning of Moscow's invasion of Ukraine, the State Department has warned U.S. citizens to immediately leave Russia over fears of harassment.

• It has also warned the Russian government may be intentionally seeking out and arresting Americans, likely as tokens in prisoner exchanges.

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