Russian President Putin and Syrian President Assad enter a hall during a meeting at the Kremlin in Moscow.

Syrian President Bashar al-Assad flew into Moscow on Tuesday for a meeting with Russian President Vladimir Putin during which the two men discussed their joint military campaign against Islamist militants in Syria, a Kremlin spokesman said.

“The president of the Syrian Arab Republic Bashar Assad came on a working visit to Moscow yesterday evening and held talks with Russian President Vladimir Putin,” the spokesman, Dmitry Peskov, told reporters.

Putin last month received parliamentary approval to launch an air campaign in the war-torn country.

News of the meeting between Putin and Assad comes after U.S. and Russian military officials signed a memorandum of understanding on Tuesday that includes steps their pilots should take to avoid an inadvertent clash over Syria as they carry out separate air strikes against militant groups, the Pentagon said.

The issue of aircraft safety started after Russia began bombing targets in Syria last month. Moscow says it is attacking Islamic State, but many of its air strikes have hit territory held by other rebel groups fighting against Russia’s Syrian ally, President Bashar al-Assad.

Pentagon spokesman Peter Cook said the full text of the memo would not be released at Russia’s request, but it included specific protocols for air crews to follow, plus the creation of a ground communications link between the two sides in the event air communications fail.

Last week, Putin said Russia would not deploy ground troops to Syria, where it has been conducting air strikes against what it says are ISIS targets.

“We are not planning on doing this (conducting a ground operation), and our Syrian friends know about this,” Putin said in an interview broadcast on state-run Rossiya-1 television channel.

He also said Russia does not want to get involved in an inter-religious war in Syria. He also explained that Russia does not see a difference between Sunni and Shiite groups.

Using modern jets and older Soviet aircraft, Russia has bombed command posts and training camps of what it says are radical “terrorists,” backing a ground offensive by Assad’s forces.

Putin had also said that Russian operation’s objective was to “stabilize the legitimate authorities and create conditions for finding a political compromise.”

Speaking of the weaponry used in the strikes — including cruise missiles Russia fired from the Caspian Sea at targets more than 1,500 kilometers (900 miles) away — Putin dismissed the idea that Russia was in an “arms race” with the West.

“This is not about an arms race,” he said. “This is about the fact that modern weapons are improving, changing. In other countries, this is happening even faster than here. This is why we have to keep up.”

According to Agence France-Presse, this is Assad’s “first foreign visit since Syria’s war broke out in 2011.”

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