Niamey - Opposition Niger presidential candidate Hama Amadou was arrested on Saturday on his return from a year in exile over allegations of baby trafficking, a party colleague said.
"He was arrested on leaving the plane. Police presented him with a warrant issued for his arrest," said lawmaker Amadou Salah.
The former prime minister and national assembly president fled the country in August last year to escape baby trafficking charges.
According to Salah, after leaving the plane Amadou "was led to a car (and taken) to an as yet unknown destination."
Security forces blocked the route and access to the area as the two-time former prime minister was driven away.
Earlier, an AFP reporter had witnessed clashes between security forces and supporters of Amadou's Modem party outside the airport.
After sporadic clashes across the day calm had returned as night fell around 19:00.
Security forces also cordoned off the party's Niamey headquarters where Amadou had planned to make an address following a parade in the city to mark his return after almost 15 months out of the country.
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On Thursday he had said: "I have decided to return to Niamey on Saturday. I have duties to my country which I plan on carrying out through my candidature" for the presidential poll whose first round is scheduled for February 21 alongside parallel legislative polls.
Announced candidates to date are incumbent President Mahamadou Issoufou and ex-planning minister Amadou Boubacar Cisse.
Ahead of his return Amadou challenged the authorities to prove their case against him.
"If a dossier has been put together against me by my opponents then it is time for me to present myself to the judges so that they say what the truth is," he said.
In mid-September Interior Minister Hassoumi Massaoudou had warned that an order had gone out to "all police units" to arrest Amadou "as soon as he sets foot on national territory."
Political tensions have been in the air for the past two years in Niger amid widespread opposition to the poll calendar drawn up by the country's electoral commission.
Opposition groups had previously criticised the constitutional court, which validates candidatures and election results, for apparent "allegiance" to President Issoufou.
The United Nations has called for "peaceful and credible" elections to be held in order to ensure stability in a country whose southern flank has been wracked by attacks by the Islamic extremist Boko Haram group. Jihadist violence has also hit regions bordering Mali and Libya.