Four Americans who were kidnapped in north-eastern Mexico crossed the border to buy medication, Mexican President Andrés Manuel López Obrador says.

The US citizens were driving through Matamoros in Tamaulipas state in a white minivan on 3 March when a group of unidentified gunmen shot at them.

They were then placed in a vehicle and taken away, the US government said.

The FBI has not confirmed the Mexican president’s statement, nor identified the missing Americans.

“There was a confrontation between groups and they were kidnapped,” Mr López Obrador said Monday.

The incident also resulted in the death of an innocent Mexican citizen, US ambassador to Mexico Ken Salazar said in a statement.

“We have no higher priority than the safety of our citizens,” the ambassador said.

“Officials from various US law enforcement agencies are working with Mexican authorities at all levels of government to achieve the safe return of our compatriots”, he continued.

Mr López Obrador said during a news conference on Monday that he had been in contact with the governor of Matamoros over the weekend about the kidnappings.

“I think it will get resolved,” Mr López Obrador said. “That’s what I hope.”

A Mexican official told Reuters three men and one woman were kidnapped.

Tamaulipas is one of six states in Mexico that the US State Department advises travellers not to visit due to “crime and kidnapping”.

The FBI is seeking help from the public and offering a $50,000 (£41,620) reward for information leading to the return of the victims and the arrests of those involved.

The Americans were driving in a van with North Carolina licence plates, according to the Federal Bureau of Investigation, which did not identify the US citizens.

Matamoros is located directly across the border from Brownsville, Texas.

According to the State Department, organised crime “including gun battles, murder, armed robbery, carjacking, kidnapping, forced disappearances, extortion, and sexual assault – is common along the northern border,” including in the state of Tamaulipas.

Criminal groups have targeted buses as well as cars driving through the state, often taking passengers and asking for ransom payments in an area where local law enforcement has limited ability to respond to crime, the State Department said.

The US government estimates that hundreds of thousands of Americans cross the border into Mexico each year to receive healthcare services, including prescription drugs. The majority of Americans cite cheaper costs as the most common reason to get treatment abroad. (BBC)