Relations between NATO allies Turkey and the United States are at their lowest ebb in recent times after Ankara vowed to retaliate against Washington's sanctions on two senior Turkish ministers.
The United States has imposed the measures in response to Turkey's failure to release American pastor Andrew Brunson who has been held in jail and now under house arrest for almost two years.
But the Brunson case is far from the only area of tension bedevilling relations between Washington and Ankara, with a list of disputes scotching hopes of any rapprochement under the presidency of Donald Trump.
- Russia -
Turkey's increasingly cosy relationship with Russia and President Vladimir Putin has alarmed both the United States and the European Union, in particular a deal for Ankara to buy Russian S-400 air defence systems.
Despite being nominally on opposite sides of the Syrian conflict, Ankara and Moscow have since late 2016 been working on a peace process aimed at ending the civil war.
The US Senate on Wednesday passed a defence authorisation bill which notably prohibits the delivery of F-35 Joint Strike Fighter aircraft to Turkey over the S-400 purchase.
But Ankara has threatened to apply international arbitration if the delivery does not go through, with presidential spokesman Ibrahim Kalin this week warning the US that Ankara had legal options to challenge any block.
- Gulen -
Turkey is increasingly frustrated that the United States has failed to hand over Fethullah Gulen, the exiled Muslim preacher Ankara blames for the 2016 attempted coup, so he can face trial at home.
Gulen, who has lived in self-imposed exile in Pennsylvania since 1999, strongly denies the charges.
Turkey has stepped up the pressure on Washington to return Gulen but the US says the conditions to detain or return Gulen have not been met, according to American law.
"They presented a very large quantity of information about the Gulen organisation and about the coup, but the issue is 'is there sufficiently clear evidence of Fethullah Gulen's personal involvement in the coup'?" a senior US official said last month.
- Prisoners -
Brunson is not the only prisoner whose detention by Turkey has angered the US.
Several Americans were caught up in the crackdown that followed the failed coup, including NASA scientist Serkan Golge, a dual national, who was jailed for seven-and-a-half years in February for being a member of Gulen's movement.
Two employees from US missions in Turkey remain in custody on terror charges and another under house arrest.
"The US has grown increasingly frustrated at the lack of Turkish progress on addressing its main complaints," said Amanda Sloat, former State Department official, now a senior fellow at the Brookings Institution.
She cited the "troubling" plans of a NATO ally to purchase a Russian missile defence system and the imprisonment on "spurious terrorism charges" of US citizens and Turkish consulate staff.
- Halkbank -
Turkey reacted with fury in January when Mehmet Hakan Atilla, 47, deputy director general of Turkish lender Halkbank, was convicted by a US federal jury in a New York court in January of helping Iran evade US sanctions on billions of dollars of oil proceeds.
The trial had heard testimony which implicated President Recep Tayyip Erdogan and other officials in the scheme. The president called the case a "plot" against Turkey.
Media reports, including in the pro-government Daily Sabah, have suggested Turks and Americans discussed swapping Atilla, who was sentenced to 32 months in jail, for Brunson.
"They already have a deal which was in the works. It's one both sides could present as a victory to their own public," Asli Aydintasbas, fellow with the European Council on Foreign Relations (ECFR) told AFP.
Halkbank also faces a massive fine from the US Department of the Treasury, which could lead to "strains in the balance of payments, pressure on the lira and a tightening of credit conditions," said Jason Tuvey, senior emerging markets economist at Capital Economics.
- Syrian Kurds -
A still unresolved issue is US support for the Syrian Kurdish People's Protection Units (YPG) militia, which controls much of northern Syria after ousting jihadists but Turkey regards as a terror group.
In January, Turkey launched an offensive supporting Syrian rebels against the YPG in its western enclave of Afrin, despite US calls for restraint.
Ankara repeatedly threatened to take the operation further to the YPG-held city of Manbij where there are US forces but, thanks to a flurry of diplomacy, the NATO allies produced a joint "roadmap" in May to coordinate security and avoid a clash.
But Aydintasbas said there was now the risk of a "pause" on Manbij. "I don't see how the (Manbij timetable) could work out with US sanctions imposed on Turkey," she added.
US President Donald Trump (L) and Turkey's President Recep Tayyip Erdogan (R), seen here at a recent NATO summit, have seen tensions between their countries rise on issues ranging from Turkey holding a US pastor to purchasing a Russian missile defence system