Ratcheting up the confrontation over the Syria war, Russia said Monday that its "volunteer" ground forces would join the fight, and NATO warned the Kremlin after at least one Russian warplane trespassed Turkey 's airspace.
The saber-rattling on both sides reflected a dangerous new big-power entanglement in the war, as longstanding differences between Russia and the United States over President Bashar al-Assad of Syria and his opponents increasingly play out not only in the halls of the United Nations but on the battlefield in Syria.
Although President Vladimir V. Putin of Russia said he would not put troops in Syria, the plan for so-called volunteers was disclosed on Monday by his top military liaison to the Parliament, Adm. Vladimir Komoyedov.
Moreover, American military officials said they believed more than 600 Russian military personnel were already on the ground in Syria, not counting aircrews, and that tents for nearly 2,000 people had been seen at Russia's air base near Latakia, in northwest Syria near the Turkish border.