Three girls staged suicide bombings in the Nigerian city of Damaturu on Friday, killing at least 13 people as residents prepared for the Eid festival at the end of Ramadan, police said.
The attacks, in a northeastern area hard hit by the Boko Haram insurgency, came just days before Nigeria's new President Muhammadu Buhari travels to Washington for talks with US counterpart Barack Obama.
The bombings came on the day the country's new army chief was due to visit the city to meet soldiers battling Boko Haram.
Buhari is expected to use Monday's meeting with Obama to push for US help to tackle the jihadist violence, which has surged since he took office in May, claiming more than 700 lives.
Boko Haram have increasingly used young women and girls as human bombs over the past year as part of campaign of terror, which has left 15,000 people dead and 1.5 million homeless since 2009.
In neighbouring Chad, a soldier and 19 Boko Haram members were killed in a shootout following an insurgent raid on an army post on Lake Chad, a Chadian security source said.
Chadian President Idriss Deby Itno said he would not back down against the Islamists, vowing: "Boko Haram will disappear one day."
In the Nigerian attacks, residents said twin explosions near a prayer ground in Damaturu killed two people, before a third blast moments later near a mosque that left another 11 dead.
Markus Danladi, Yobe state police commissioner, confirmed 13 people were killed.
"The attacks were carried out by three underage girls. Fifteen people were also injured in the attacks."
Army spokesman Sani Usman however gave a toll of nine dead and 18 injured, adding: "Troops and security agencies responded immediately to the incidents. The situation is currently under control."
The attacks followed a double bombing at a market in the town of Gombe, south of Damaturu, on Thursday that killed at least 49 people who were shopping for the Eid celebrations.
This year's Ramadan has been particularly deadly, with suicide bombers hitting mosques and worshippers gunned down as they prayed.
"There were two blasts near the Eid prayer ground," said Ahmad Adamu, a security volunteer in Damaturu said of Friday's attacks.
"The first blast went off around 7:15 am (0615 GMT) while security volunteers... were waiting for the worshippers so they could assist in crowd control," he said.
"While we were attending to the victims we heard another blast about 500 metres (yards) away."
Damaturu is the capital of Yobe, one of three northeastern states worst affected by the insurgency.
Nigeria's new army chief Major General Tukur Buratai was due to visit Damaturu on Friday to celebrate Eid with soldiers battling the jihadists, who have pledged allegiance to the Islamic State group that has seized swathes of Iraq and Syria.
Buhari, a former military head of state, has made the fight against Boko Haram one of the main planks of his administration. He has sacked the military top brass he inherited from his predecessor and Buratai was named to the post only this week.
Topping the agenda of Buhari's talks with Obama "will be measures to strengthen and intensify bilateral and international cooperation against terrorism in Nigeria and west Africa", according to the Nigerian presidency.
Relations suffered in the latter part of former Nigerian president Goodluck Jonathan's rule, with Abuja considering US aid to fight Boko Haram insufficient.
The west African nation decided to halt a US training programme for an army battalion which would have developed into a unit to take on the militants.
The Islamist militants have taken advantage of the transitional period between Buhari's installation and the deployment of a regional force of 8,700 troops, scheduled for late July, to launch deadly attacks on an almost daily basis.
The group has also carried out suicide bombings in neighbouring Chad and Cameroon.