MOSCOW - The Kremlin sharpened its accusations Wednesday in the aftermath of Turkey's downing of a Russian warplane, as Moscow's top diplomat called the incident a "planned provocation" that has dealt a major blow to already fragile relations with NATO.

But Foreign Minister Sergei Lavrov also tamped down speculation of a military response by Russia after the jet broke apart in flames along the Turkish-Syrian border. "We're not going to war against Turkey," he said after talks with his Turkish counterpart.

Still, Russia moved to strengthen its forces in Syria, saying new antimissile systems would be deployed at an air base less than 20 miles from the Turkish frontier.

Lavrov's comments offered the clearest signals that Moscow views the downing as more than an accident while Russia steps up its airstrikes in Syria to support the embattled government of President Bashar al-Assad.

Turkey and its Western allies have backed rebel groups seeking to topple Assad in Syria's nearly five-year civil war. Pentagon officials, meanwhile, have raised worries about possible accidental contact between Russia's air campaign and a U.S.-led coalition conducting airstrikes against the Islamic State.

"We have serious doubts this was an unintended incident and believe this is a planned provocation," Lavrov said after discussions with Turkey's foreign minister, Mevlut Cavusoglu.

Lavrov said the plane was fired on after "making extremely effective strikes on the oil tanker trucks and oil fields."

Earlier, Russian officials said one of two Russian pilots shot down has been rescued following the first downing of one of their planes by a NATO ally since the Cold War. The other airman was killed "in a savage way" by militiamen, claimed Russia's ambassador to France, Alexandre Orlov.

During the search-and-rescue mission, a Russian Mi-8 helicopter was blown up, apparently by an antitank missile fired by Syrian rebels, killing one Russian marine. It marked the first confirmed deaths of Russian soldiers in combat in Syria.

In a show of Russia's deepening military involvement, it now plans to deploy powerful S-400 antimissile systems to Russia's Khmeimim air base in northwestern Syria. The batteries - with a range of 250 miles - have the potential to create headaches for Turkish and other aircraft in the U.S.-led coalition targeting the Islamic State.

Russian President Vladimir Putin, meanwhile, set some limits on Russia's military role, promising not to send ground troops to help bolster Assad.

In Moscow, protesters pelted the Turkish Embassy with eggs and stones.