LAGOS - Two American and two Canadians who were kidnapped in an ambush by gunmen in northern Nigeria this week were freed on Saturday, police said.

Nigerian armed forces had launched a manhunt for the four after they were seized on Tuesday evening in the state of Kaduna by kidnappers who shot dead two of their police escorts.

"They have been rescued thanks to the efforts of the police," Kaduna state police spokesman Muktar Aliyu said. "All of them are a good condition of health," he said, and are now with their embassies.

One person has been arrested, he added.

The four North Americans were on private business in Kaduna when they were snatched on the road from the town of Kafanchan to the state capital of Abuja, the latest abduction in Nigeria involving foreigners.

Aliyu said they were rescued at about 5 am (0400 GMT) in the same area where they were kidnapped.

"I cannot confirm if there have been negotiations or a ransom paid," Aliyu said, adding that it was "classified information". A State Department travel advisory urges US citizens to "reconsider" travelling to Nigeria, warning that "violent crime such as armed robbery, assault, carjacking, kidnapping and rape is common throughout the country". Kidnapping has long been a problem in Nigeria's southern states, where high-profile individuals, including the families of prominent politicians, are regularly seized. But as the economy stalled in recent years, the crime began creeping north.

A crackdown on cattle rustling has been blamed for rising numbers of abductions in the north, with criminals turning to kidnapping.

The Kaduna-Abuja road is notoriously unsafe. It is a journey of about two-and-a-half hours by car through villages and past tracts of fields and forests.

Security on the route came under intense scrutiny last year when the federal government announced the closure of the capital's only airport for essential runway repairs.

Many foreign missions and companies advised staff to limit their travel during the closure period, as all domestic and some international flights were switched to Kaduna.

In July 2016, Sierra Leone's defence attaché to Nigeria was kidnapped by men in military fatigues armed with AK-47 rifles at a fake checkpoint on the Abuja-Kaduna road.