Some analysts say Russia appears to have arrived at an accommodation in which the Turks are moving to establish a security zone in northern Syria to preclude Syrian Kurds from setting up an autonomous region. In return, the Turks appear to be backing off their efforts to unseat President Bashar al-Assad of Syria, who, with Russian help, is strengthening his hold on the country’s major cities to the south.
“The Russian-Turkish rapprochement is largely tactical,” said James F. Jeffrey, a former United States ambassador to Turkey. “Russia can live for now with a Turkish enclave in northern Syria if it does not threaten the Assad regime. And it allows Russia to exploit the U.S. shift to Turkey’s rival, the Y.P.G., by providing air support to the Turks against the Islamic State, which the U.S. inexplicably is not providing.”
President-elect Donald J. Trump has spoken positively, though in vague terms, about the possibility of cooperating with Russia in the fight against the Islamic State, also known as ISIS or ISIL. But the Obama administration’s efforts to forge a common political and military strategy with the Kremlin on Syria collapsed after Russia supported Syrian forces and Iranian-backed fighters with its air power in the brutal retaking of Aleppo.
Turkey began the operation at Al Bab, east of Aleppo, without coordinating with the United States and without the benefit of American airstrikes. “This is something that they’ve decided to do independently,” Col. John Dorrian, the spokesman for the American-led operation against the Islamic State, said in November.
Turkey appeared to have assumed that it would make short work of the Islamic State fighters there. But the fighting has been stiff. In late November, the Turkish military’s problems were compounded when three of its soldiers were killed in what Turkish forces said was a Syrian airstrike.
Mr. Erdogan later spoke by phone with Vladimir V. Putin, the Russian president, who assured him that Russia had not been involved in the air attack, according to Turkish news reports. The improving ties between the two autocratic leaders opened the door to greater cooperation.
The Turkish military spoke publicly about the Russian role in a Jan. 2 statement that noted that Russian warplanes had struck targets the previous day about five miles south of Al Bab. American officials, who asked not to be identified because they were discussing intelligence, said that Russian airstrikes in the Al Bab area began at the end of December, and that Russian aircraft were flying near Al Bab as recently as Friday.
The effectiveness of the Russian air operations, which have mainly involved dropping “dumb,” or unguided, bombs, is unclear. As Turkey’s casualties have mounted in the Al Bab operation, Turkish officials have complained about the lack of American air support and have even made veiled threats that Turkey might suspend allied combat flights against the Islamic State in Iraq and Syria from its major base at Incirlik, which would be a major blow to the American-led air campaign.
American officials suggested that the holdup in carrying out allied airstrikes in recent weeks was related to a Turkish decision to ban the Americans from flying reconnaissance drones in and around Al Bab to help identify and confirm targets, as well as bad weather. The Turkish military said that measure was needed to ensure that no potentially hostile aircraft flew over its troops, but it has hampered the United States’ ability to carry out airstrikes without endangering civilians.
Operating without the benefit of precise intelligence, the United States recently engaged in what officials called a “show of force” operation in which American aircraft flew low over Al Bab and dropped flares. But last week, the Turks agreed that the United States could fly drones and other aircraft to gather intelligence, which paves the way for the American-led coalition to carry out airstrikes against the Islamic State in Al Bab, American officials said.
The United States regards the Kurdish forces as some of the most effective fighters in the campaign against the Islamic State in Syria. But in deference to Turkish sensitivities, the Americans have declined to arm them directly. The Turks, however, regard them as nothing more than an arm of the Kurdistan Workers’ Party, an insurgent Kurdish group in Turkey and Iraq. The Turks have blamed the group for killing dozens of Turkish security forces in recent weeks.
By any measure, the nascent cooperation between Russia and Turkey is a striking development. The situation was far different when Russian warplanes arrived at Latakia, Syria, in September 2015 to help the Assad government take on rebel groups, including some backed by the United States and Turkey.
Relations were thrown into a crisis after a Turkish fighter jet shot down a Russian Su-24 attack plane and the Russian pilot was fatally shot by Syrian rebels as he was parachuting down. Mr. Putin denounced the shoot-down as a “stab in the back.” Russia responded by deploying the S-400, an advanced air-defense system, at Latakia, and imposed economic sanctions against Turkey.
But over the past year, the calculations of the two countries have changed. While President Obama warned that Syria would become a Russian military “quagmire,” the Russians, working with Iran, Iranian-backed forces and the Syrian military, helped Mr. Assad take back Aleppo in the waning months of the Obama administration without substantial Russian casualties.
Still, Russia has to reckon with the fact that the Syrian military lacks the troops to control all of the country. At the same time, Turkey’s immediate objectives have shifted. Worried about the possibility that Kurdish fighters might link up separate cantons to establish an autonomous enclave across northern Syria, as well as about the presence of Islamic State fighters near its borders, Turkey sent its own forces into northern Syria in August.
The Turkish offensive, which has enlisted the support of Syrian opposition groups that Turkey has backed, succeeded in taking the town of Jarabulus. But it has become bogged down near Al Bab, the last major town west of Raqqa still held by the Islamic State.
The Russians notified the United States about the flights using a special hotline between Russian forces in Syria and the American air war command at Al Udeid Air Base in Qatar. The hotline’s goal is to “deconflict” air missions carried out by the Russians and the American-led coalition.