Nigerian authorities came under fire on Sunday over the decision to postpone national elections in the face of relentless Boko Haram violence, with the opposition branding the move a "major setback for democracy."

Some observers charged that the political woes of President Goodluck Jonathan -- facing an increasingly strong election challenge from ex-military ruler Muhammadu Buhari -- were the real reason for the delay.

Nobel peace laureate Malala Yousafzai on Sunday called for global support to help release more than 200 Nigerian schoolgirls kidnapped by Boko Haram, as they marked 300 days as hostages.

"As we mark this tragic 300th day of captivity for hundreds of kidnapped Nigerian schoolgirls, I call on people everywhere to join me in demanding urgent action to free these heroic girls," she said.

Campaigning in Nigeria's knife-edge presidential election entered its final week on Saturday, with mounting questions about whether the vote will even go ahead and persistent security fears.

President Goodluck Jonathan, battered by criticisms over his handling of the Boko Haram crisis, corruption and the economy, is seeking a second four-year term of office.

Boko Haram launched its first major attack in Niger on Friday, triggering a forceful response from regional troops who claimed to have killed more than a hundred of the Islamists.

The clashes in Bosso and Diffa, along the border with Nigeria, marked yet another expansion of violence attributed to Boko Haram, but it seemed to have come at a heavy cost.

Boko Haram militants on Friday launched an attack on a border town in Niger that left a number of people dead, the first such assault in the country by the Islamists now being hunted by regional forces.

Soldiers repelled the assault on the town of Bosso, but it marked yet another expansion of violence attributed to Boko Haram, which has waged a worsening six-year insurgency centered in northeastern Nigeria. 

Whoever wins Nigeria's February 14 election will take charge of an economy battered by falling oil prices, leaving the new administration with fewer options to tackle the twin crises of poverty and unemployment, analysts said. 

President Goodluck Jonathan's government has over the last four years sought to paint a picture of Nigeria's prosperity rising. 

Niger is set to send troops to Nigeria for the multi-national battle against Boko Haram after scores of people were killed in a fresh onslaught by the Islamist fighters in a key border town.

Intervention from Niger would open a new northern front in the increasingly regional fight against the Islamist insurgents who killed more than a hundred people, including 19 soldiers, on Wednesday in a rampage in the Cameroonian town of Fotokol on Nigeria's border.

Niger is set to send troops to Nigeria for the multi-national battle against Boko Haram after scores of people were killed in a fresh onslaught by the Islamist fighters in a key border town.

Intervention from Niger would open a new northern front in the increasingly regional fight against the Islamist insurgents who killed over a hundred people, including 19 soldiers, on Wednesday in a rampage in the Cameroonian town of Fotokol on Nigeria's border.

Pirates have hijacked a crude oil tanker off the Nigerian coast, taking three hostages and killing the vessel's Greek deputy commander, the Greek coastguard said Wednesday.

The Malta-flagged Kalamos was anchored and awaiting fresh cargo from Qua Iboe, an oil terminal in Nigeria's southeastern region operated by ExxonMobil, when it was boarded on Tuesday.

Nigerian Boko Haram fighters went on the rampage in the Cameroonian border town of Fotokol Wednesday, massacring civilians and torching a mosque before being repelled by regional forces.

The onslaught came a day after Chad sent troops across the border to flush the jihadists out of the Nigerian town of Gamboru, which lies some 500 meters (yards) from Fotokol on the other side of a bridge.