As Russia started delivering to Turkey a missile defence system in a deal that has angered the US, here is a recap of the fallout and repair of bilateral relations.

- 'Stab in the back' -

In November 2015, two Turkish military jets shoot down a Russian warplane over the Turkey-Syria border, resulting in the death of a pilot.

Russia rejects Turkey's assertion that the plane, deployed in support of the Syrian regime's fight against rebels, had strayed into Turkish airspace.

President Vladimir Putin slams a "stab in the back" and Moscow announces a raft of economic sanctions against Ankara, including in agriculture, tourism and construction.

- Turkish regret -

There is a thaw in late June 2016 when President Recep Tayyip Erdogan expresses regret about the incident and calls for friendlier ties.

The Kremlin says he also apologised.

After their first telephone call since the incident, Putin announces an end to the tourism bans and the normalisation of trade ties.

The following month he is among the first international leaders to offer Erdogan support after a failed coup rocks his country.

- Gas pipeline go-ahead -

In August 2016, the two men meet in Saint Petersburg, Putin saying afterwards their countries had "lived through a very complicated moment" but wanted to overcome their "difficulties".

In October, Russia and Turkey sign an agreement to build the TurkStream gas pipeline that will pump Russian gas under Turkish waters in the Black Sea towards Europe.

Construction starts in March 2017.

- Together on Syria -

In January 2017, Russia, Turkey and Assad-backer Iran launch talks in Astana, Kazakhstan to end the Syrian conflict.

It sidelines the United States, with which both have strained ties.

Several rounds result in agreement on four "de-escalation" zones in Syria, leading to a decrease in violence in some areas.

Even though Russia backs the regime and Turkey is behind the rebels, they forge strong cooperation over Syria.

- 'Most important partner' -

In March 2017, Putin and Erdogan announce the "normalisation" of ties. "We consider Turkey our most important partner," Putin says.

They sign a new economic cooperation plan and pledge to continue cooperation notably in the fight against the Islamic State (IS) group active in Syria.

At the end of May, Putin orders the lifting of most remaining sanctions on Turkey.

- Russian defence system -

In September 2017, Turkey signs a deal with Russia to buy its S-400 surface-to-air missile defence systems, its first major weapons purchase from Moscow.

It raises concern with Ankara's allies in the NATO military alliance.

In December, Russia announces negotiations are finalised with delivery scheduled for 2019.

- Nuclear plant accord -

In April 2018, the two presidents launch construction of Turkey's first nuclear power station, to be built by Russia's state atomic energy cooperation Rosatom.

The Akkuyu nuclear power plant is expected to be operational by 2023.

- New Syria deal -

In September 2018, they agree to create a "demilitarised zone" around Syria's Idlib region in a bid to avert a military assault on the last rebel and jihadist bastion in the country.

Syrian forces and their Russian allies, however, step up strikes on the hold-out areas from April 2019.

- Joint defence production -

In May 2019, Erdogan says Turkey and Russia will jointly produce the next generation S-500 defence systems.

There is "absolutely no question" of stepping back from the S-400s purchase, he adds, after Washington had threatened sanctions if the deal went ahead.