Lagos - Thousands of Nigerians have been blocked from travelling abroad in a bid to stop them becoming involved in foreign terrorism, prostitution or other criminal activity, immigration officials said on Tuesday.
Almost 24,000 nationals aged 17 to 35 were turned back at the border between January 2014 and March this year, the Nigerian Immigration Service (NIS) told AFP.
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"There have been reports in recent times of some Nigerians departing to join terrorist groups especially in the Middle East and north Africa," said NIS spokesman Chukwuemeka Obua.
The crackdown sought to prevent young Nigerians being "lured into terrorism, prostitution, slavery and other untoward activities abroad", the NIS said in a statement.
Nigeria is struggling to end a six-year insurgency by Boko Haram Islamists that has claimed more than 15,000 lives and displaced 100 times that number in the north-east.
But the country has also become a "catchment area for recruiters" abroad because of high unemployment, the NIS said.
Among the most high-profile Nigerians convicted for overseas terror offences is 28-year-old Umar Farouk Abdulmutalab, a failed suicide attacker with connections to Al-Qaeda, popularly referred to as the "Underwear Bomber".
He was hailed as a hero by Al-Qaeda chief Osama Bin Laden after trying to blow up a Northwest Airlines flight from Amsterdam to Detroit, Michigan, on Christmas Day 2009 and is serving four life terms in the United States.
Nigerian media reported at the weekend that two cousins from Kano in the north were caught at the weekend trying to cross from India into Pakistan, with eventual plans join up with the Islamic State group in Iraq.
The NIS said foreign terrorist organisations had syndicates to arrange travel documents, visas, tickets and money for their Nigerian recruits.
"To counter this, the NIS now engages in intense profiling of travellers. We have always had problems of Nigerians going abroad for greener pasture," it added.
"We look at the age of the intending traveller and the person he is travelling with, put them by the side and profile them thoroughly."
More than 5.3 million people left or arrived in Nigeria between Janaury 2014 and March this year, according to the NIS.
Around 10,000 Nigerians were deported from abroad during the same period while 3,793 others were refused entry into countries overseas.