ABUJA (AFP) - Protesters on Thursday took their call for the release of more than 200 schoolgirls kidnapped by Boko Haram to Nigeria's president, as US military personnel headed to Chad as part of the rescue effort.

About 200 protesters, most of them wearing red, set off for the Presidential Villa of Goodluck Jonathan, calling for the government to do more in the search and rescue efforts.

They were prevented by police from getting close to the gates of the villa but a government delegation, including ministers, met them and delivered a statement from Jonathan, reports an AFP correspondent at the scene.

The Nigerian leader restated the government's commitment to finding the girls.

"(The) government believes that we must all come together to fight terrorism and that protest should be directed at the terrorists who have abducted our innocent daughters and deprived them of a place at the fountain of freedom in our country," the statement read.

The protesters told the government delegation they were not satisfied with Jonathan's response.

"You have to tell Mr President that the answers we have received are not adequate. Please let Mr President know that none of the issues raised has been addressed," march organiser, Obi Ezekwesili, a former education minister and World Bank executive, said.

"Our proposal is that we will demand of Mr President another opportunity of a meeting that addresses the issues that citizens have put before our Commander-in-Chief," she stated.

Previous street protests in Abuja have led to meetings with lawmakers at the national parliament, Nigeria's national security adviser and military top brass.

But the demonstrators claimed that police prevented them from reaching the president's residence.

Thursday's march came after US President Barack Obama announced that 80 military personnel had been deployed to Chad to help find the 223 girls still missing since their abduction on April 14.

Obama said in a letter to Congress that the military contingent would stay in Chad until their support in ending the crisis that has triggered worldwide outrage "is no longer required".

"These personnel will support the operation of intelligence, surveillance and reconnaissance aircraft for missions over northern Nigeria and the surrounding area," he wrote.

The deployment marks a significant boost to an existing US military effort which includes the use of surveillance drones as well as manned aircraft over Nigeria.

US defence officials said MQ-1 Predator as well as Global Hawk unmanned aerial vehicles were being used. Both were unarmed, although the Predator has been used against the Taliban in Afghanistan and the tribal badlands of Pakistan.

The Pentagon has criticised Nigeria for failing to react quickly enough to the rise of Boko Haram, who have been blamed for thousands of deaths since 2009.

Jonathan's administration had previously resisted close cooperation with the West but accepted help from US, British, French and Israeli specialists amid a groundswell of pressure fuelled by a social media campaign.

Nigeria is hoping to tighten the screws on Boko Haram and has asked the United Nations Security Council to proscribe the group, which is said to have links to Al-Qaeda-linked militants in north Africa.

Jonathan has called the extremists "Al-Qaeda in western and central Africa", underlining what Nigeria views as Boko Haram's threat to regional stability.

The United States and a number of other countries have already designated Boko Haram as a terrorist organisation in an attempt to cut off any international support and overseas funding for the group.

Many state-run schools were shut Thursday on the orders of the Nigerian Union of Teachers (NUT) to allow a "day of protest" against the abduction of the girls from Chibok on April 14.

In the last five weeks, Boko Haram has stepped up its campaign of attacks outside the northeast worst affected by the insurgency, leading to fears of an escalation of violence across the country.

Hours before the girls' kidnapping, the group bombed a crowded bus station in the Abuja suburb of Nyanya, killing 75. A copy-cat bombing at the same location on May 1 left 19 dead.

On Tuesday, two car bombs ripped through a busy market within 20 minutes of each other in the central city of Jos, killing at least 118. There are fears that the death toll could rise further.

The bombing - Nigeria's deadliest - was seen by experts as an indication of Boko Haram's intent to export violence and demonstrate their capability to the international community.

"They have sleeper cells all over the northern part of the country and they're activating them," said Kyari Mohammed, a Boko Haram specialist and chairman of the Centre for Peace Studies at Nigeria's Modibbo Adama University.

At the same time, there has been no let-up in the bloodshed in Borno state, one of three in the northeast which has been under a state of emergency since May last year.

More than 50 people were killed in three separate attacks this week.

Two were near Chibok on Monday and Tuesday, while the third was near Gamboru Ngala, close to Lake Chad, where a reported 300 people were killed last month.