A suicide bomb attack by a young girl in the northeast Nigerian city of Maiduguri has killed 19 people, while another a bomb-laden car exploded in Yobe state, killing a further two people, police said.

The first blast happened at about 12:40pm local time (11:40 GMT) on Saturday near the live chicken section of the city's Monday Market, AFP news agency said.

The attacker was believed to be a girl as young as 10 years old, according to sources quoted by AFP news agency.

Al Jazeera's Ahmed Idris, speaking from Abuja, quoted police as saying there were six deaths while another 20 people were injured. The attack had not yet been claimed. 

A second blast occured at about 3:30 pm (14:30 GMT) on Saturday in the Potiskum Area Command. 

Our correspondent Idris said that there were conflicting reports but that police sources said that the car bomb had detonated while being searched by policemen as the owner was being questioned in the police station. 

"It was while they were at the gates of the police station undergoing security checks that the car exploded," an officer, who spoke on condition of anonymity told AFP news agency. 

"The policeman and the driver have been confirmed dead but details of other casualties are not clear yet," he said.

'Deadliest' attack

The bombing occurred a day after violence in Baga, another town in Borno on the border with Chad, left about 2,000 people - mostly children and women - dead, according to Amnesty International, the UK-based human-rights organisation.

The numbers of people killed have not yet been independently confirmed, but the conflict in Baga on Friday, being blamed on Boko Haram, is reportedly among the worst in Nigeria in six years.

Daniel Eyre, Nigerian researcher for Amnesty International said in the organisation's statement called that attack "Boko Haram's deadliest act in a catalogue of increasingly heinous attacks carried out by the group."

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"If reports that the town was largely razed to the ground and that hundreds or even as many as two thousand civilians were killed are true, this marks a disturbing and bloody escalation of Boko Haram's ongoing onslaught against the civilian population," he said.

The town and at least 16 nearby settlements in and around Lake Chad were burnt to the ground and at least 20,000 people forced to flee their homes, AFP news agency reported.

The US has condemned the spike in the Boko Haram-related attacks saying that the attackers must be held accountable. 

"The United States condemns the recent escalation of attacks on civilians carried out by Boko Haram, which shows no regard for human life. All those responsible for these recurring terrorist attacks must be held accountable," the US State Department said in a statement late on Friday.