The United States has called on all parties in Turkey to support President Recep Tayyip Erdogan's government against a coup attempt by the military - with other world leaders expressing concern about the upheaval in a Nato member country.

President Barack Obama and Secretary of State John Kerry spoke by phone and gave their support to Mr Erdogan.

“The President and Secretary agreed that all parties in Turkey should support the democratically-elected government of Turkey, show restraint, and avoid any violence or bloodshed,” the White House said in a statement.

The situation remains unclear but there have been numerous reports of violence.

A spokesman for the German government said on Twitter: "The democratic order must be protected, all must be done to protect lives."

In neighbouring Greece, the armed forces and police are holding emergency meetings in Athens to monitor developments. Officials described the country's armed forces as being placed in a state of "heightened readiness" and not alert.

Moscow expressed grave concern about events in the country, and it had instructed officials to help Russian nationals in Turkey return home at the earliest opportunity. Kremlin spokesman Dmitry Peskov told reporters President Vladimir Putin was being kept constantly updated on the situation.

Turkey coup - 60 dead in 'act of treason' against the government

Peskov said events were moving too fast to fully understand what was happening, but he said Russia was concerned and wanted to see Turkey return to the path of stability and order, and for there to be a lawful outcome.

In the UK, Foreign Secretary Boris Johnson said he was “very concerned” about the events.

The Foreign and Commonwealth Office has urged people to “avoid public places and remain vigilant.”

A Nato official at alliance headquarters in Brussels told The Associated Press early Saturday that "we're following events closely," but said he had no other comment. The official spoke only on condition of anonymity because he was not authorized to make public statements.

Nothing in Nato's founding 1949 Washington Treaty says anything about intervening in the internal or political affairs of an alliance member, and Turkey kept its NATO membership following past military coups.

The United Nations is also trying to clarify the situation. "The Secretary-General is closely following developments in Turkey. He is aware of the reports of a coup attempt in the country,” spokesman Farhan Haq said.

"The United Nations is seeking to clarify the situation on the ground and appeals for calm."

Responses elsewhere were a marked contrast. In Syria, Hundreds of cheering people took to the streets of Damascus early on Saturday and celebratory gunfire erupted. around the Mazzeh district of the Syrian capital, with people waving flags and shouting: "God, Syria and Bashar!". There were similar celebrations in other government-held cities.

Mr Assad's government has accused Mr Erdogan of fuelling Syria's five-year conflict by supporting Islamist insurgents battling Damascus and allowing foreign jihadis to cross the border from Turkey into Syria.