The European Union risks compromising human rights if it fails to ensure Turkey offers proper protection to all refugees under a deal to curb flows to Europe, the United Nations' human rights chief said Tuesday.

The EU is pushing for an initial agreement this week with Turkey to start taking back refugees and migrants reaching Europe from its shores. The U.N. and rights groups have criticized the notion of mass returns to Turkey, which restricts Geneva Convention rights for refugees to Europeans.

"We believe that Turkey should lift all restrictions on Geneva," said U.N. High Commissioner for Human Rights, Zeid Ra'ad Al Hussein.

Some diplomats in Brussels suggested a declaration from Turkey that it would treat everyone in line with the standards of the Geneva Convention would be enough, but Zeid disagreed.

"We would rather see that full protections are provided," he said. "There are many concerns we have about the human rights situation in (Turkey), we need to feel assured that the full protection is given to those who merit it."

Zeid said for any deal to be in line with international law, it had to ensure each case was individually assessed, and he also warned that pushing asylum processing centers offshore could turn them into "centers of abuse".

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He said Turkey, which now houses some 2.5 million people fleeing the conflict in neighboring Syria, should also take proper care of people who do not satisfy the definition of a refugee but require protection including children, the disabled, victims of trafficking or sexual abuse.

Zeid said he had received assurances on Tuesday from the EU's executive arm deputy head, Frans Timmermans, and the bloc's foreign policy chief, Federica Mogherini, that any final deal with Turkey would respect EU law.

"The risk is that if, for the sake of expediency, the EU defaults on its human rights obligations, then the reputation as being one of the principle standard-bearers upholding human rights around the world would be affected," he said.

"If the EU is perceived to cut corners when it comes to international law and European standards, it can have a knock-on effect on other parts of the world."

The refugee crisis has opened deep rifts between the EU's 28 member states and fueled support for nationalists and populists.