China's Foreign Ministry on Tuesday said it would work with Pakistani authorities to investigate reports the two Chinese nationals abducted by the militant Islamic State (IS) group in Quetta were missionaries.

Ministry spokesman Lu Kang in a statement said China attached great importance to protecting the safety and legal rights of Chinese nationals overseas, but must adhere to local laws and regulations and respect local traditions and customs.

"As for reports that the relevant Chinese nationals were suspected of illegal missionary work in Pakistan, we will cooperate with the Pakistan government and launch an investigation in accordance with the law," Lu said.

The pair, identified by authorities as Lee Zing Yang, 24, and Meng Li Si, 26, were abducted by armed men pretending to be policemen on May 24 in Quetta. Last week, IS' Amaq propaganda agency claimed its members had killed them.

The kidnapping was a rare crime against Chinese nationals in Pakistan but it has alarmed the growing Chinese community in the country.

The Interior Ministry on Monday alleged for the first time that the two were preachers who had abused the visa system by posing as business people to enter the country.

“Instead of engaging in any business activity they went to Quetta and under the garb of learning Urdu language from a Korean national... were actually engaged in preaching,” the ministry said in a statement.

It did not say what kind of preachers they were, nor did it say if the Korean was from North Korea or South Korea.

In his statement, Lu reiterated that China opposed all forms of terrorism and commended the Pakistan government's pledge to continue protecting Chinese people and businesses in the country.