By Hader Glang

ZAMBOANGA CITY, Philippines

Philippine authorities have held 10 Pakistanis traveling in the archipelago’s troubled south after they failed to present proper documents, according to an official Thursday.

Lt. Cmdr. Alvin Dagalea, Coast Guard station chief, told reporters the Pakistan nationals -- who identified themselves as businessmen and their wives -- were heading by ferry from Zamboanga City to the island province of Basilan -- a stronghold of the Daesh-linked Abu Sayyaf militant group.

They were turned over to the Bureau of Immigration on Tuesday.

The Philippines' maritime borders with Malaysia and Indonesia, known as the "southern backdoor”, have long been used as entry points for illegal activities, including by smugglers, pirates, kidnap-for-ransom gangs and militants.

"They [10 Pakistanis] are currently under the custody of proper authorities as they failed to present any valid documents when our coast guard personnel requested their identification during the pre-departure inspection on a ferry, docked at a local port in this city [Zamboanga]," Dagalea said Thursday.

The five men and five women instead presented a letter dated Feb. 23 and signed by an Alibasher Usman who claimed to be “committee on information, ticketing and visa extension head” of a mosque in Marawi, a majority Muslim city east of Zamboanga.

According to Dagalea, the letter said the Pakistanis were visiting the Philippines upon the invitation of Usman’s group, described as “purely a non-profit, non-political and non-violent religious organization”.

Philippine authorities are still investigating the authenticity of the letter as well as the identity of “Usman”.