Dorjkhorol Amarbold, 20, Lkharvasura Orgilsuren, 34, Ganzorig Khosbayar, 22, Ayush Shinekhuu, 32, Sereeterbat Munkhtsetseg, 30, and Tsetsegmaa Chimgee, 29, are being investigated for "stealing properties," a crime punishable by up to 15 years in jail, media reports said.

Vietnamese law treats theft as a criminal offense if the stolen property's value exceeds VND2 million ($87).

Initial investigations show that crime police officers in District 1 were patrolling the downtown area last Sunday when they began following four Mongolians who were acting suspiciously.

On Ly Tu Strong Street, they caught Dorjkhorol unlocking a fanny pack of a 44-year-old Japanese man and stealing an iPhone while three others, Lkharvasura, Ganzorig and Ayush, kept a lookout. The cops swooped down on the four pickpockets and detained them.

On Tuesday, a 49-year-old Japanese man filed a complaint with the management board of the Independence Palace that he lost a wallet while visiting the historical site.

Based on camera footage, security guards spotted two Mongolians, Sereeterbat and Tsetsegmaa, and detained them till the police arrived.

At the police station, officers found $404 in cash on Sereeterbat and around $130 on Tsetsegmaa.

Police are investigating further.

In the first nine months of this year, Vietnam’s southern metropolis received 6.2 million international tourist arrivals, up 14 percent from a year ago. However, street crimes, robbery and rip-offs continue to sully the city’s image.