ISLAMABAD, Pakistan — Pakistan sent 30 migrants back to three European countries on Thursday after refusing to allow them to disembark from a chartered plane at an airport in Islamabad, officials said, a move that reflected growing frustration over the treatment of asylum seekers.

Sarfraz Hussain, a spokesman for the Pakistani Interior Ministry, described the migrants as “unverified deportees,” most of whom were sent back from Greece, saying the authorities would not permit anyone to enter the country without proper documentation.

A Greek police official, speaking on the customary condition of anonymity, said all 49 passengers on the plane were Pakistani citizens. “They had Pakistani Embassy documents,” he said. “Why would Pakistani Embassy staff give documents to people who are not from Pakistan?”

The Pakistani interior minister, Chaudhry Nisar Ali Khan, said last month that European countries were sending people back to Pakistan without identifying their nationality. But the episode Thursday was the first time that the country had refused to admit deportees.