In this frame grab provided by Russian Defence Ministry press service, Russian long range bomber Tu-22M3 flies during an air strike over Aleppo region of Syria on Tuesday, Aug. 16, 2016. Russia's Defense Ministry said on Tuesday Russian warplanes have taken off from a base in Iran to target Islamic State fighters in Syria. (Russian Defence Ministry Press Service photo via AP)
In this frame grab provided by Russian Defence Ministry press service, Russian long range bomber Tu-22M3 flies during an air strike over Aleppo region of Syria on Tuesday, Aug. 16, 2016. Russia's Defense Ministry said on Tuesday Russian warplanes have taken off from a base in Iran to target Islamic State fighters in Syria. (Russian Defence Ministry Press Service photo via AP)

Beirut — Iran allowed Russian warplanes to take off from its territory to bomb targets in Syria on Tuesday, an unprecedented move that underscores the deepening cooperation between two powerhouses heavily invested in the Syrian civil war.

The Iranian deployment increases Russia’s foothold in the Middle East and widens Moscow’s bombing campaign in Syria, bolstering President Bashar Assad’s government ahead of a new round of peace talks the United Nations hopes to convene in coming weeks.

The long-range bombers took off early Tuesday near the Iranian city of Hamedan, 175 miles southwest of the Iranian capital, and struck targets in three provinces in northern and eastern Syria, the Russian Defense Ministry said.

The Russian warplanes then returned to Russia and no Russian forces remained stationed in Iran, according to a U.S. official, speaking on condition of anonymity because the official was not authorized to speak about the matter.

“Russia’s use of an Iranian base represents a turning point in Russia’s relations in the Middle East. … It sends a powerful message to the United States and regional powers that Russia is here to stay,” said Fawaz Gerges, professor of international relations at the London School of Economics.

Russia had talked about the possibility of flying planes out of Iran since late last year, but its decision to do so on Tuesday came as a surprise, U.S. officials said.

Col. Christopher Garver, a U.S. military spokesman in Baghdad, told reporters at the Pentagon on Tuesday that the Russians activated a communications link with coalition officials just ahead of the bomber mission.

“The Russians did notify the coalition,” he said, adding that they “informed us they were coming through” airspace that could potentially put them in proximity to U.S. and coalition aircraft in Iraq or Syria.

Asked how much advance notice the Russians gave the U.S., Garver said, “We did know in time” to maintain safety of flight.

U.S. officials said the setup at the Iranian air base occurred very quickly, perhaps overnight. One military official said the Russians flew four Tu-22 Backfire bombers to the Iranian air base, along with a Russian cargo plane loaded with the munitions for the bombers, just hours before the bombers flew their missions. The officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

It is virtually unheard of in Iran’s recent history to allow a foreign power to use one of its bases to stage attacks. Russia has also never used the territory of another country in the Middle East for its operations inside Syria, where it has been carrying out an aerial campaign in support of Assad’s government for nearly a year.

Tuesday’s action suggests cooperation on the highest levels between Moscow and Tehran, both key allies of the embattled Syrian president, and sends a powerful message to the United States and the Sunni monarchies of the Gulf, which have seen Iran as the arch-enemy.

The Russian move provides a psychological boost for the Assad-Iran-Hezbollah alliance, illustrating that Russia is strategically committed to stay on course in Syria.

It also heralds even more intense Russian bombardment of Syrian cities.