Vladimir Putin

The two leaders were conversing on the sidelines of the Group of 20 summit here, according to a US National Security Council spokesman. More details about their discussion were expected later Monday, but US officials said before the summit that Syria and Ukraine would likely be on the agenda of an Obama-Putin huddle.

The two leaders spoke as they sought to mend ties over the November incident that saw Moscow slap sanctions on Ankara, and reportedly agreed on the phone to meet in person.

"Reiterating their commitment to reinvigorate bilateral relations and fight terrorism together, the two leaders agreed to remain in contact and meet in person," the Turkish presidency said in a statement.

The International Association of Athletics Federation (IAAF) decided not to lift the suspension, imposed after accusations of state-sponsored doping.

Individual athletes can compete as neutrals if they prove they are clean.

The Russian president called on other bodies, including the International Olympic Committee (IOC), to intervene.

The IOC executive board said it would hold a telephone conference on Saturday to discuss the issue ahead of a full IOC summit in Lausanne on Tuesday.

The United States launched a ground-based missile defense system earlier this month in Romania. The system is meant to defend Europe against rogue states like Iran and not intended to target Moscow's missiles, Washington has said.

Putin issued his threat during a news conference Friday after meeting with Greek Prime Minister Aleksis Tsipras in Athens.

The EU is expected to renew sanctions in a matter of weeks.

Alexis Tsipras was speaking at a joint news conference in Athens with the Russian President Vladimir Putin.

Mr Putin said there would be "no discussions" about Crimea, the Ukrainian peninsula that was seized by Kremlin-backed forces in 2014, leading to sanctions from the EU and US.

The territory, which has an ethnic Russian majority, later voted to join Russia in a referendum that Ukraine and Western countries deem illegal.

He said the Russian intervention had largely achieved its objectives.

The comments come amid fresh peace talks in Geneva aimed at resolving the five-year Syrian conflict.

Russia is a key ally of Syrian President Bashar al-Assad and his office said in a statement he had agreed to the move.

The pullout was "in accordance with the situation on the ground", the statement said.

Russia began its campaign of air strikes in Syria last September, tipping the balance in favour of the Syrian government and allowing it to recapture territory from rebels.

The statement was made to the Associated Press by Iraqi government officials. 

Obama made his remarks at a White House news conference Friday.

The president called Russia's military involvement, including airstrikes that began this week, a self-defeating exercise that will move the Syrian conflict further from a solution.

Ministry spokesman Igor Konashenkov told Russian news agencies on Wednesday that Russian jets are carrying out targeted airstrikes on the positions, vehicles and warehouses that Russia believes belong to IS militants.

Russia's upper chamber of parliament earlier on Wednesday gave the green light to President Vladimir Putin's request to send Russian troops to Syria.

Syrian newspapers said the speech drew "clear outlines" for what is needed to "fight terrorism" on a global level.

In his address Monday in New York, Putin urged the world to stick with Assad, saying it was a "huge mistake" not to engage the Syrian military in the fight against the Islamic State group.