Turkish President Recep Tayyip Erdogan arrived Wednesday in Beijing amid tensions over China’s treatment of its Uighur minority and sensitive negotiations surrounding the possible purchase of a Chinese missile system.

While the sides enjoy outwardly friendly relations, Turkish public sentiment has been inflamed by reports that members of the Uighur minority native to China’s northwest have been restricted in practicing their Islamic faith, particularly during the holy fasting month of Ramadan, which ended in mid-July.

Turks and Uighurs share close linguistic, cultural and religious ties.

Hundreds of people marched in Istanbul earlier this month, burning Chinese flags outside the Chinese consulate, waving flags representing the Uighurs’ putative homeland and calling for a boycott of Chinese goods. The demonstration was peaceful but a group of nationalists tried to attack a group of Korean tourists which they mistook for Chinese nationals. Police rescued the tourists.

Prior to the protests, the Turkish Foreign Ministry had called in the Chinese ambassador and issued a statement saying the Turkish public was “saddened” by reports of the Ramadan restrictions.

China responded by denying any curbs on religious expression and demanding that Ankara clarify the matter.

Despite Beijing’s statements, China has exercised long-standing bans on Uighur Communist Party members, government workers and students joining in religious observances.

Erdogan was due to meet with Chinese President Xi Jinping following a formal welcoming ceremony.

Relations between the two are further complicated by Turkey’s closeness with the United States and the ongoing civil war in Syria.

Turkey, a member of the North Atlantic Treaty Alliance, agreed in principle in 2013 to buy China’s HQ-9 air defense missile system. China reportedly offered the best price and offered to furnish the technology behind the system.

However, the deal has run into controversy over its incompatibility with NATO weapons systems and the possible leak of military secrets to Beijing.

China has also opposed any international intervention in Syria, while Erdogan has been among the toughest critics of Bashar Assad’s regime.

The differences come despite growing tourism and surging Chinese exports to Turkey, which has contracted with a Chinese company to build a high-speed rail line. Al Arabiya