The American consulate in the most populous Turkish city of Istanbul issued a notice Saturday warning of an "imminent security threat" against the diplomatic compound. The warning came as Turkey grapples with heightened political tensions and an increasing number of terrorist attacks targeting civilians and security forces.

"We strongly encourage U.S. citizens to maintain a high level of vigilance, be aware of local events and take the appropriate steps to bolster your personal security," a a State Department agency said in a statement.

Turkey has endured a number of security threats in recent months. A pipe bomb set off on a highway overpass in Istanbul Tuesday injured five civilians and set city residents on edge. Turkish authorities suspected the intended target had been a bus full of police officers, a frequent target of politically motivated attacks by Kurdish dissident groups. There has been no claim of responsibility for the attack. 

That bombing came 2 1/2 months after a pair of suicide bombers killed more than 100 demonstrators at a peace rally in the Turkish capital of Ankara. Attributed to forces aligned with the Islamic State group, the attacks fueled increased acrimony between the ruling AK Party and Kurdish political factions, some of which have faced violent reprisals from the government. 

The Overseas Security Advisory Council, the U.S. State Department agency that issued the security warning Saturday, exists to protect private American business interests in foreign jurisdictions.

This isn't the first time the U.S. consulate in Istanbul has faced security concerns. In August, two women apparently assaulting the compound were reportedly shot there amid a spate of attacks throughout Istanbul that left nine dead. Nobody associated with the consulate was harmed at that time.