Abuja - Relatives of over 200 schoolgirls kidnapped by Boko Haram militants marked 500 days on Thursday since the abductions, with hope dwindling for their rescue despite a renewed push to end the insurgency.
The landmark comes amid a worsening security crisis, where Islamists have stepped up deadly attacks since the inauguration of President Muhammadu Buhari, killing more than 1,000 people in three months.
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Boko Haram fighters stormed the Government Secondary School in the remote town of Chibok in Borno state on the evening of April 14 last year, seizing 276 girls who were preparing for end-of-year exams.
Fifty-seven escaped but nothing has been heard of the 219 others since May last year, when about 100 of them appeared in a Boko Haram video, dressed in Muslim attire and reciting the Koran.
Boko Haram leader Abubakar Shekau has since said they have all converted to Islam and been "married off".
The Bring Back Our Girls social media and protest campaign staged a youth march in Abuja to mark the grim anniversary and have announced plans for an evening candle-lit vigil.
Dozens of young campaigners known as the "Chibok Girls Ambassadors" processed through the streets of the capital dressed in their signature red t-shirts, many with red ribbons tied to their hair and around their heads.
Joined by prominent clerics and other well-wishers, they carried placards bearing the names of the missing girls and banners displaying their pictures and campaign slogans.
"My heart bleeds for the children. I feel terribly ashamed," said Abuja's Catholic archbishop John Onaiyekan, dressed in his red cardinal's robes.
"I feel ashamed that about 300 girls should disappear just like that, even after we have been told that the military are doing very well, that they are making progress, routing the terrorists, scattering their camps."
Sheikh Nura Khalid, chief imam of the capital's Apo Mosque said he would be challenging all fellow Muslim clerics to "use our pulpits to be preaching for the freedom of the Chibok girls".
The mass abduction brought the brutality of the Islamist insurgency unprecedented worldwide attention and prompted a viral social media campaign demanding their release backed by personalities from US First Lady Michelle Obama to the actress Angelina Jolie.
Nigeria's government was criticised for its initial response to the crisis and Western powers, including the US, have offered logistical and military support to Nigeria's rescue effort, but there have been few signs of progress so far.
The military has said it knows where the girls are but has ruled out a rescue effort because of the dangers to their lives.
Global sex trade
Boko Haram, blamed for killing more than 15,000 people and forcing some 1.5 million to flee their homes in a six-year insurgency, has rampaged across Borno since Buhari came to power on May 29, vowing to crush the insurgency.
The fresh wave of violence has dealt a setback to a four-country offensive launched in February that had chalked up a number of victories against the jihadists.
An 8,700-strong Multi-National Joint Task Force, drawing in Nigeria, Niger, Chad, Cameroon and Benin, is expected to go into action soon.
In a report published in April, Amnesty International quoted a senior military officer as saying the girls were being held at various Boko Haram camps, including in Cameroon and possibly Chad.
The Chibok abduction was one of 38 the rights group has documented since the beginning of last year, with women and girls who escaped saying they were subject to forced labour and marriage, as well as rape.
Fulan Nasrullah, a respected Nigerian security analyst and blogger who claims specialist knowledge of the inner workings of Boko Haram, told AFP there was "no hope" of ever recovering most of the Chibok girls.
"Most have had kids by now and are married to their captors. Many have been sold into the global sex trade and are probably prostituting in Sudan, Dubai, Cairo and other far flung places," he said.
"Some have been killed probably in attempts to escape, air strikes on camps where they were being held, et cetera."