The Turkish government this week deported foreigners working with Syrian refugees at a leading U.S.-based aid organization, part of what appears to be an ongoing crackdown on international humanitarian groups there.

The four foreigners — from Britain, Ireland, Indonesia and India — were among 15 employees of the International Medical Corps (IMC) detained since April 20 by Turkish police in Gaziantep, the southern Turkish city where many organizations aiding millions of Syrian refugees in Turkey are based. The other 11 — all Syrians — remain in a detention camp, according to an IMC statement.

The actions came as President Recep Tayyip Erdogan, whose narrow victory in an April 16 referendum vastly expanding his powers has been questioned by political opponents and international election monitors, has continued to intensify a battle against perceived enemies at home and abroad.

The government on Wednesday detained more than 1,000 people suspected of backing a Turkish cleric blamed for a failed military coup last summer, adding to as many as 100,000 who have been detained or arrested since then.

Erdogan has also been engaged in skirmishes with the United States, including a Turkish airstrike Tuesday that killed as many as 20 U.S.-backed Kurdish fighters inside Syria. After the Trump administration accused the Turks of failing to consult on their air activities, Turkey said Wednesday that it had consulted with all relevant U.S. military and diplomatic agencies.

In response, the Pentagon said that Turkey’s notification — less than an hour before the strikes — did not amount to consultation under agreements between the NATO allies. Turkey considers Syrian Kurds, who are in the vanguard of U.S. proxy forces on the ground against the Islamic State, to be terrorists.

The reason behind the crackdown on humanitarian groups was not clear. Since late last year, pro-government media in Turkey have published allegations against international organizations, saying that some are involved in abusing refugees, including turning children against their parents and stealing body parts. Turkey also objects to humanitarian assistance going to Kurds in Syria.

In early March, the government ordered Oregon-based Mercy Corps to shut down its operations there, ending a program that provided regular assistance both to hundreds of thousands of refugees and to civilians besieged inside Syria. Other, smaller aid groups have also been shut down, and many received indications their required annual registration may not be renewed.

The 15 IMC staff members have valid Turkish work permits, and the organization is registered with the Turkish government. Asked to appear to present their paperwork to Gaziantep police, they were then taken to a detention center there.

Rebecca Gustafson, senior communications adviser for the organization, said in a statement that IMC is “working with the Turkish government to secure the release of those staff still detained as soon as possible, and we continue to support our team members and their families during this very difficult time.”

IMC, with approximately 320 employees in Turkey, has been working with Syrian refugees there since 2012, providing primary medical care and mental health support, as well as job training and business workshops, among other forms of assistance.

Separately, Wednesday’s mass arrests, part of a government purge of the state’s institutions, were among the largest in months. The government has accused a Turkish cleric, Fethullah Gulen, who lives in exile in Pennsylvania, of orchestrating the July coup attempt and has demanded his extradition. Gulen denies any role in the attempt.

The latest sweeps targeted “secret imams” suspected of being part of a Gulen network that infiltrated police forces, Interior Minister Suleyman Soylu said. Later Wednesday, Turkey’s national police agency said in a statement that more than 9,000 police personnel had been suspended from their jobs as part of the investigation into suspected Gulenists.

[In divided Turkey, president defends victory in referendum granting new powers]

The government’s referendum platform relied in large part on the notion that the new powers would give Erdogan a freer hand to move against the state’s enemies, including Gulenists, the Islamic State and Kurdish militants affiliated with Turkey’s Kurdistan Workers’ Party, or PKK.

The changes, which transform Turkey’s government from a parliamentary to a presidential system, have been harshly criticized by Erdogan’s opponents, who say it cements his increasingly tight hold on power.

Fahim reported from Istanbul.

Read more:

What Erdogan’s narrow referendum victory means for Turkey

He’s 77, frail and lives in Pennsylvania. Turkey says he’s a coup mastermind.

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