Story highlights The two Chinese nationals were kidnapped last month and killed

Protecting the 20,000 Chinese residing in Pakistan is posing a challenge

(CNN) Two slain Chinese nationals who were kidnapped in Pakistan in May and whose deaths ISIS has claimed responsibility for had been missionaries and the "misuse" of their business visas contributed to their abductions and deaths, Pakistan's interior minister said.

Amid "deep concern over the unfortunate incident," Interior Minister Chaudhry Nisar Ali Khan on Monday ordered a review of its visa policies and called for the establishment of a database of Chinese nationals.

The man, 24, and woman, 26, killed were among a group of Chinese citizens who obtained a business visa from the Pakistani Embassy in Beijing, the ministry statement said.

Instead of doing business, it is alleged the pair went to the Pakistani city of Quetta and under the guise of learning Urdu from a Korean, they "engaged in preaching," the Pakistani statement said.

The statement did not elaborate on what kind of preaching the two were engaged in.

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