MOSCOW — Russia condemned on Monday the American military’s downing of a Syrian warplane and suspended the use of a military hotline that Washington and Moscow have used to avoid collisions in Syrian airspace. Russia also threatened to target aircraft flown by the United States and its allies over Syria.
The Russian military has halted cooperation in the past — notably after President Trump ordered the launch of missiles against a Syrian air base in April — and it was not clear whether the latest action would be lasting. Nonetheless, it was the most recent example of the intensifying clash of words and interests between the two powers, which back different sides in Syria’s civil war.
An American F/A-18 jet shot down the Syrian government warplane south of the town of Tabhah on Sunday, after the Syrian aircraft dropped bombs near local ground forces supported by the United States. It was the first time the American military had downed a Syrian plane since the civil war began in the country in 2011.
In response, the Russian Defense Ministry called American attacks against the Syrian forces “military aggression” and announced that it would suspend cooperation with the United States intended to prevent airborne accidents over Syria.
“All flying objects, including planes and drones of the international coalition, detected west of the Euphrates, will be followed by Russian air defense systems as targets,” the Russian Defense Ministry said in a statement.
Weeks after President Vladimir V. Putin ordered Russian military forces to Syria in September 2015 to prop up the regime of President Bashar al-Assad, Russia and the United States signed a memorandum on preventing air incidents between the two countries.
Since then, the agreement has been a crucial link that has allowed Moscow and Washington to coordinate their military actions in the region, in which Iran, Israel, Russia, Syria, Turkey, and the United States with its allies carry out attacks in pursuit of often competing aims.
However, the agreement has also appeared to provide leverage for Moscow each time the situation has threatened to escalate.
After Mr. Trump ordered the attack on the Syrian air base in April, Russia said it would suspend the agreement. But weeks later, the Russian and American militaries continued to use the hotline, with the number of calls increasing, American officials said.
Speaking in Beijing on Monday, the Russian foreign minister, Sergey V. Lavrov, seemed to be unaware of the decision. He called on the United States and all other countries involved in the Syria conflict to “coordinate their actions.”
“We urge everyone to avoid acting unilaterally, to respect the sovereignty of Syria,” Mr. Lavrov said.
In Moscow, Frants Klintsevich, the deputy chairman of the Russian Senate’s defense committee, called the downing of the Syrian warplane a “blunt act of aggression and provocation.”
“It is Russia that is being provoked most of all,” Mr. Klintsevich wrote in a Facebook post. “It seems that the U.S. under Donald Trump is the source of danger for the Middle East and the whole world on a qualitatively new level.”