Mercy Corps, a leading American charity that uses Turkey as a base to aid hundreds of thousands of civilians upended by the war in neighboring Syria, was forced to curtail its work on Wednesday after the Turkish government abruptly revoked its registration to operate.

“Our hearts are broken by this turn of events, which comes after five years of cooperation with the government of Turkey and other local partners,” Mercy Corps said in a statement.

It said Turkish officials had provided no explanation for the move, which forced Mercy Corps to “shut down our operations in Turkey, effective immediately.”

Mercy Corps, a global organization with programs in more than 40 countries, has run one of the largest humanitarian operations in the Syrian conflict. Since 2012, it has been delivering lifesaving assistance to as many as 500,000 civilians in Syria each month, much of it through Turkey. In 2016, the charity also provided emergency help to 100,000 Syrian and Turkish civilians on Turkey’s side of the border.