A delegation of senior American officials arrived in Ankara today for talks aimed at ending the row between Turkey and the United States which has led to a suspension of visa services. "This situation must come to an end as it is not a sustainable situation," said Turkish Deputy Prime Minister Bekir Bozdag. "It will be in the interest of both countries for the visa crisis not to be extended further," he added. Last week relations plunged between the NATO allies after Washington stopped issuing non-immigrant visas at its missions in Turkey following the arrest of a US consulate employee over alleged links to the group accused of launching last year's failed coup. Turkey responded with a tit-for-tat measure and President Recep Tayyip Erdogan last week blamed outgoing US ambassador to Ankara John Bass for the suspension. The American delegation will meet Turkish foreign, justice and interior ministry officials tomorrow, Bozdag told reporters in Ankara. "Turkey-American relations have passed very strong tests, but we have never faced such incidents like the visa crisis in any period," Bozdag said. Turkish prosecutors summoned another local employee working at the American consulate in Istanbul last week, whose wife and daughter had been detained. The staffer's whereabouts remain unknown but Turkish officials last week claimed he was hiding in the Istanbul consulate, which Bass denied. The wife and daughter were released by an Istanbul court today, but banned from leaving the country, state-run news agency Anadolu reported. Jonathan Cohen, Deputy Assistant Secretary for European and Eurasian Affairs, is leading the American delegation, Anadolu said. Turkish officials had long expressed the hope of improving Ankara-Washington ties under US President Donald Trump, after they eroded badly during the final months of Barack Obama's administration. The two countries have been at odds over US support for the Syrian Kurdish militia fighting the Islamic State extremist group in northern Syria and Washington's failure to extradite Pennsylvania-based Muslim cleric Fethullah Gulen. Ankara accuses Gulen, who has lived in self-imposed exile since 1999, is blamed by Ankara for last year's failed coup in Turkey, a charge which he strongly denies. Erdogan and other Turkish officials have been careful not to blame Trump for the latest straining of ties. Last month Trump gave the Turkish leader "high marks" for "running a very difficult part of the world".