Suicide bombers attacked an open-air praying area in northeastern Nigeria on Friday, killing at least 13 people in Damaturu, police said.
Officials said the bombings were carried out by an elderly woman and a 10-year old girl. They said other underage girls might have been involved in the attack.
The militant group Boko Haram has increasingly used young women and girls as human bombs, raising fears that the group is forcing some of its hundreds of captives to carry out its attacks.
The explosions Friday struck an area where worshippers were observing Eid al-Fitr, the end of the holy month of Ramadan. At least 15 others were injured in the attack.
A bombing in Gombe city Thursday killed about 50 people. That attack took place in a market crowded with customers doing some last-minute shopping for the festival marking the end of a month of fasting.
No one has claimed responsibility for the two attacks, but they resemble those carried out by Boko Haram, which has killed thousands in a six-year insurgency in the country's northeast.
The United States strongly condemned the bombings Thursday and Friday and reiterated its commitment to help Nigeria and its neighbors counter Boko Haram.
There has been a spike in attacks by Boko Haram since a four-nation coalition of Nigeria, Niger, Chad and Cameroon pushed out the militants from captured territory earlier this year.
The violence intensified after Nigeria's new president, Muhammadu Buhari, took power a month and a half ago and vowed to crush the group, something his predecessor also had made a priority but failed to do.
Buhari travels to Washington on Monday for a meeting with President Barack Obama that is expected to focus on how the United States can help fight Boko Haram.
Earlier this week, Buhari replaced all of Nigeria's military chiefs in another step aimed at halting the insurgency. The new army chief and national security adviser come from Borno, a step welcomed by the state governor, Kashim Shettima. He said the new generals understand the terrain and can easily connect with communities to get local support.
"Nigeria now has the best of chances to overcome the challenges of insurgency facing it since 2009," the governor said.
