For most of the 20th century Turkish authorities were happy to lend their treasures for foreign exhibitions and ignored the provenance of most pieces in Western collections. Today, however, the government argues that any object without the correct permissions or with gaps in its provenance has been stolen and so belongs to Turkey.

Growing economic power and stalled talks over EU membership make many Turks feel that it is time to turn their backs on the West. Amid the turmoil of the Arab spring Turkey believes it can become the leader of the region. “A new Middle East is about to be born,” Ahmet Davutoglu, the foreign minister, told parliament last month. “We will be the owner, pioneer and the servant of this new Middle East.”

Turkey has been inspired by the success of Italy and Greece in confronting the illicit trade in classical antiquities. Officials also cite the tough stance taken by Zahi Hawass, a colourful former Egyptian minister, against museums with dodgy holdings. “We will make life miserable for museums that refuse to repatriate,” he pronounced at an international 2010 conference in Cairo about looted artefacts.

Turkey has been emboldened by two important successes. Last September the Boston Museum of Fine Arts bowed to public pressure and returned the top half of an 1,800-year-old statue called “Weary Herakles”, which came from southern Turkey. Left to the museum by an American couple, its documented provenance went back no more than 30 years, which suggests it was looted, probably in the late 1970s. Mr Erdogan himself brought this trophy back to Turkey, reuniting the head and torso with the statue’s bottom half.

Mr Gunay also forced the German government to return a massive sphinx (pictured) that had been removed in 1917 from Hattusa, the Bronze-Age capital of the Hittite empire. The sphinx is one of a pair. The first was sent back to Turkey in 1924. Its twin had long been part of the permanent display at the Pergamon museum in Berlin. Germany maintained it had obtained the sphinx legally, whereas Turkish authorities argued that it had merely been sent to Germany for repair. Documentation about the sphinxes was destroyed in bombing raids on Berlin in the second world war.

Early last year Turkey stepped up the pressure, indicating that it would not renew the licences of the German archaeology institute, the biggest foreign group working in Turkey, unless the sphinx was sent home. In May 2011 German and Turkish culture officials signed an agreement to return the sphinx as part of a wider accord on training curators, exchanging research and enabling loans of Turkish objects. But German curators now complain that as soon as the sphinx went back to Turkey the rest of the agreement was quietly shelved.

The Turkish authorities then turned their attention to the Metropolitan Museum of Art. In September 2011 a delegation led by Murat Suslu, the director-general for cultural heritage and museums, flew to New York to discuss loans for a 2014 exhibition. Mr Suslu, who has a reputation as a table-thumper, opened the meeting with a declaration of intent. Before any further loans could be discussed, he wanted information about 18 works in the Met’s collection. “It certainly came as a surprise to us,” says the Met’s director, Thomas Campbell, “especially in light of the collaborative spirit we have always enjoyed with our peer institutions in Turkey.”

Within weeks, the focus was on the BM. The Topkapi Museum had agreed to an important loan for an exhibition about the Haj that the BM was planning for January 2012. The 35 pieces under discussion had been removed from Mecca by the Ottoman authorities in the 19th century. At the last moment, Mr Suslu and Mr Gunay refused to allow the loan to go ahead on the grounds that the BM had a stone tablet dating from the first century BC, known as the Samsat Stele, that originally came from Turkey. The stele had been in the BM’s collection for almost 90 years (and had been exhibited, without complaint, at a Tokyo exhibition in 2005 alongside loans from the Topkapi).