Russia and Turkey have taken a big step towards normalising relations, with their leaders announcing an acceleration in trade and energy ties at a time when both countries have troubled economies and strains with the West.
President Vladimir Putin received his Turkish counterpart Tayyip Erdogan in a Tsarist-era palace outside his home city of St Petersburg on Tuesday, Erdogan's first foreign trip since last month's failed military coup which left Turkey's relationship with the United States and Europe badly damaged.
The visit is being closely watched in the West, where some fear both men - powerful leaders ill-disposed to dissent - might use their rapprochement to exert pressure on Washington and the European Union and stir tensions within NATO, the military alliance of which Turkey is a member.
Putin said Moscow would gradually phase out sanctions against Ankara, imposed after the Turks shot down a Russian fighter jet near the Syrian border nine months ago, and that bringing ties to their pre-crisis level was the priority.
"Do we want a full-spectre restoration of relations? Yes and we will achieve that," Putin told a joint news conference after an initial round of talks.
"Life changes quickly."
Cooperation would be increased on projects including a planned $US20 billion ($A26.15 billion) gas pipeline and a nuclear power plant to be built in Turkey by the Russians, Erdogan said, as well as between their two defence sectors.
"God willing, with these steps the Moscow-Ankara axis will again be a line of trust and friendship," Erdogan said.
The leaders were to discuss the war in Syria, over which they remain deeply divided, in a subsequent closed-door session where progress is likely to be more halting - with Moscow backing President Bashar al-Assad and Ankara wanting him out of power.
Turkey has been incensed by what it sees as Western concern over its post-coup crackdown but indifference to the bloody putsch itself, in which rogue soldiers bombed parliament and seized bridges with tanks and helicopters. More than 240 people were killed, many of them civilians.
Putin's rapid phone call expressing his solidarity to Erdogan in the wake of the failed putsch had been a "psychological boost", the Turkish president said.
Turkish officials, by contrast, warned on Tuesday of rising anti-American sentiment and of risks to a crucial migrant deal with Europe, in a sign of deteriorating relations.
Erdogan blames Fethullah Gulen, a Muslim cleric who has lived in self-imposed exile in the US state of Pennsylvania since 1999, and his followers for the failed coup.
Turkey has launched a series of mass purges of suspected Gulen supporters in its armed forces, other state institutions, universities, schools and the media, prompting Western worries for the stability of the NATO ally.
In Washington, the US State Department criticised charges in the Turkish press that a Washington think tank had been behind the coup attempt.
Despite the timing of the Russia visit, Ankara has insisted that Erdogan's meeting with Putin is not meant to signal a fundamental shift in Turkish foreign policy.
Turkey hosts American troops and warplanes at its Incirlik Air Base, an important staging area for the US-led fight against Islamic State militants in neighbouring Iraq and Syria.
