The Chinese nationals, reportedly abducted and killed by Islamic State militants, were offered security by the interior ministry but they refused to accept the offer.

The ministry has also cancelled the visa of a South Korean national who it had earlier linked to the abduction incident.

Interior Minister Chaudhry Nisar was earlier told that the Chinese couple had gone to Quetta and were engaged in preaching under the garb of learning Urdu from a Korean national, Juan Won Seo, who is the owner of ARK Info Tech.

 It was revealed during the investigation, the ministry said on Friday, that Seo alias Gilbert came to Pakistan on a business visa but set up an Urdu academy and was "engaged in illegal activities".

"Police had not only cautioned the Chinese couple about the security situation but offered them protection but the Chinese individuals had refused the offer," read the ministry statement issued on Friday.

Security and intelligence agencies were closely looking into the background of the incident and reviewing photos of the kidnapped pair released on social media so they could reach some conclusion and it could also be confirmed whether the Chinese nationals were actually killed or not, the statement said, quoting ministry sources.

The ministry said earlier this month the Chinese couple Lee Zing Yang, 24, and Meng Li Si, 26, had been missionaries posing as language teachers, in violation of visa rules, and that had contributed to their abductions.

China said it would investigate whether the couple had been working as missionaries in a country which is 98 per cent Muslim.

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

The incident has prompted Pakistan to boost security around Chinese and other foreigners. Quetta is the capital of Balochistan, a region where China is investing billions of dollars in infrastructure projects.