Two American and two Canadian citizens were kidnapped in Nigeria's northern state of Kaduna on Tuesday. Two policemen, who were with the four abductees at the time of the incident, were killed by the kidnappers in the ambush. 

State police spokesperson Mukhtar Aliyu said Tuesday the four travelers were seized by armed assailants in Kaduna region at 7 p.m. (1800 GMT). Aliyu said they were considering every possible means to ensure safe release of the foreigners.

The foreigners were travelling in two separate vehicles from Kaduna to Nigeria's capital Abuja, when they were reportedly attacked. The officials refused to comment further on the details of the victims.

The U.S. state department official said they were aware of the incident in Nigeria and ensuring the safety of the kidnapped citizens was currently their top priority.

Global Affairs Canada, which manages Canada's diplomatic and consular relations, was aware of the kidnapping of two Canadian citizens in Nigeria, spokesman John Babcock informed BBC news.

"Consular officials in Nigeria are in contact with local authorities to gather additional information," he added.

In recent years, Kaduna was under intense scrutiny for a rapid increase in kidnapping cases. Earlier this month, the U.S. state department travel advisory had urged citizens to reconsider travelling to Nigeria amid severe safety concerns, since violent crimes were rampant in the region.

Kidnapping posed a regular threat in Nigeria where high profile individuals were seized and ransomed for money. The victims were usually released once the ransom was paid.

Four British missionaries were kidnapped last year in Nigeria. Ian Squire, a missionary, was abducted and killed, while three others were released after the west African country’s authorities negotiated their release.

Last year, two German archeologists were kidnapped by gunmen at a remote dig near Janjala village in Kaduna state. They were abducted at gunpoint and two villagers who tried to aid the victims were killed in the process. The abductors demanded 60 million naira ($200,000) in exchange for the prisoners. The archeologists were freed by the security agents.

In October, an Italian priest was abducted by gunmen in southern Nigeria. The 63-year-old priest was stationed in the region for three years. The priest and his group, which consisted of four other people, were ambushed and robbed by gunmen while travelling in Benin city. The priest was kidnapped while the other four were not. The priest was later released to the authorities.

Crime has spread across the country, leading to a standstill in its economy. Kidnapping has morphed into a longstanding problem in Nigeria since the crackdown on cattle rustling in the region. Cattle rustling has led to an increase in abduction cases in the area, Guardian reported. People turned to kidnapping to escape poverty wrought over losing the herd over a decade long conflict between the herder and the farmers over grazing and watering rights.