AHMEDABAD: Police in Punjab and Gujarat said Friday they were working to track down the kingpins of a people smuggling ring uncovered when French authorities halted a planeload of passengers bound for Nicaragua.

The Airbus A340 was detained last week at Vatry airport, east of Paris, where it had stopped for refuelling.

It had arrived from the United Arab Emirates and was halted after an anonymous tip-off that it was carrying potential victims of human trafficking, with most of the 303 people aboard flown back to India on Monday.

Passengers had paid between "400,000 to 1.2 million rupees" ($48,000-150,000) to agents to help them reach the southern border of the United States from South America , Gujarat state police superintendent Sanjay Kharat told AFP.

"We want to know how these people came in contact with the agents, or whether the agents contacted them, and what their plan was after reaching Nicaragua," he said.

Of the 276 passengers returned to India, Kharat said 66 were from his state, and police were in the process of interrogating them.

"We have identified people who could give us some information into the illegal racket and they are being questioned," he said.

Most of the flight's other passengers were from Punjab, where police said they were also conducting a probe.

"We are duty bound to investigate if any illegalities are brought to our notice and we are examining the issue," additional director general of Punjab police LK Yadav told AFP.

Another Punjab police official, speaking on condition of anonymity, said officers were trying to understand the scale of the racket and its links to local immigration agents.

The flight was operated by Romanian charter company Legend Airlines, and passengers were put up at Vatry airport during the investigation.

Among those staying behind in France were two people questioned by police there over suspected human trafficking.

A French judicial source said they were released after it was established the passengers had boarded the plane of their own free will.

Another 25 passengers sought asylum in France including five minors.

French authorities are continuing to investigate the case for a potential violation of immigration laws, but no longer for people trafficking, judicial sources said.

Close to 100,000 illegal Indian migrants have attempted to enter the United States this year, according to US Customs and Border Protection data.