Oren Dorell

USA TODAY

Russia on Wednesday turned to Twitter to justify its deployment of advanced S-300 anti-aircraft missile systems to Syria.

The tweet, posted by the official Twitter account of the Russian embassy in Washington, @RusEmbUSA, was attached to photos of White House spokesman Josh Earnest and an S-300 missile battery with the caption “…because you never really know what kind of assistance terrorists might get.”

“All jokes aside, #Russia will take every defensive measure necessary to protect its personnel stationed in #Syria from terrorist threat,” the tweet said.

The message reinforces previous warnings against United States' interference with a combined Russian and Syrian air campaign in Syria. The U.S. says Russian and Syrian aircraft have targeted primarily opposition forces and civilian areas in Syria, especially in the northern city of Aleppo, where several hospitals have been bombed and a United Nations aid convoy was hit on Oct. 19., killing 20 people.

The recent bombing campaign, which ended a Sept. 12 cease-fire brokered by the U.S. and Russia, is the worst in Aleppo’s history and marks an escalation by Russia and its ally. The State Department has said the Obama administration is considering various options, including a military response. Secretary of State John Kerry has warned Russia that one result of its actions could be that “more Russian aircraft will be shot down.”

The timing, however, weeks before a close presidential election, makes it unlikely the U.S. will embark on a military adventure in the waning months of President Obama’s last term. It may be a warning to the next president, whether it be Republican Donald Trump or Democrat Hillary Clinton. Trump's running mate, Gov. Mike Pence of Indiana and Clinton have expressed support for imposing a no-fly zone to protect civilians in Syria.

"The Russian move might be more a message to Hillary and Trump, to make the battle space in Syria to look too dangerous," said Michael O'Hanlon, a military analyst at the Brookings Institution, a think tank in Washington, D.C.

The missile system the Russians are touting is an excellent ambush weapon that adds a significant threat to U.S. air operations in Syria, unless American leaders are willing to accept a few losses, O'Hanlon said. Even if U.S. aircraft use radar jamming devices, the S-300, which works in a network connected by fiber-optic cables, can develop a picture of the battle space using the signal of U.S. aircraft trying to jam enemy radar.

"It can easily shoot down a U.S. fighter jet with virtually no warning," he said. "I’ve never heard an American military or intelligence official poo poo the S-300."

The S-300 deployment would also change the kind of no fly zone that a future president might impose, O'Hanlon said.

Rather than shooting down aircraft, as the U.S. did in Iraq during the 1990s, grounding aircraft in the presence of S-300 systems is more likely to focus on destroying runways, fuel depots and aircraft on the ground, while avoiding Russian personnel.

In the wrong hands, it could also threaten military and civilian air traffic in neighboring countries that are U.S. allies.

Here are five things we know about it:

Range and capability: Versions of the S-300 have a range of 250 miles, at Mach 7.5 (7.5 times the speed of sound)

Who has the missiles in the Middle East: Russia has talked for years of selling its premier air defense system to Iran and Syria. Deployments in Iran began last month.

Why they are controversial: The system’s range would extend into the territory of neighboring states, including Turkey, which shot down a Russian fighter jet last year, Iraq, where the U.S. is conducting air strikes against the Islamic State, Jordan, which also conducts air strikes in Iraq, and Israel, which has conducted several air strikes in Syria to prevent the transfer of “game changing” weapons to Hezbollah, the Lebanon-based Shiite militia backed by Iran.

How would Syria’s neighbors react? Israel sees S-300 as a “game changing” weapon and therefore a legitimate target, and has vowed to do what it must to preserve its freedom to operate over Syria and Lebanon. But Israel is unlikely to conduct a strike that would harm Russian operators or advisers.

Where have they been used before? While it’s not clear if an S-300 was involved, the missile can be fired from a BUK system, which includes sensors and launch vehicles. Such a system is suspected in the downing of the Malaysian Airlines Flight 17, which crashed in eastern Ukraine in 2014. A recent Dutch report said the system traveled from Russia before the shootdown, and later returned to Russia.

The incident, which resulted in 298 deaths, is a potent example of what could go wrong.