DAMATURU, Nigeria (Reuters) - Two suicide bombers, an elderly woman and a 10-year-old girl, killed at least nine people in the northeastern Nigerian city of Damaturu on Friday morning as worshippers gathered to mark the Muslim Eid al-Fitr holiday, a military spokesman said.

They detonated their bombs at around 7.40 a.m. (0240 ET) as worshippers queued for security screening to enter an open-air praying area in Layin Gwange, Damaturu, Colonel Sani Usman said.

“Four persons died in the first explosion and seven people were injured. While in the second explosion, five people lost their lives and 11 people were wounded,” he said.

There was no immediate claim of responsibility but such incidents are usually blamed on Islamist group Boko Haram. On Thursday, some 50 people were killed in bomb attacks at a market in Gombe, about 200 km (120 miles) from Damaturu.

Boko Haram has killed thousands of people and left about 1.5 million others displaced during a six-year insurgency in which it has tried to set up a state adhering to strict sharia law in the northeast of Africa’s most populous country.

President Muhammadu Buhari has made defeating the insurgents his top priority but since he was inaugurated on May 29 hundreds have been killed in bombings and attacks concentrated in the northeast of Africa’s top oil producer.

Buhari replaced his defense chiefs on Monday as part of an attempt to step up the campaign against the militant group and the insurgency is likely to be high on the agenda when he meets U.S. President Barack Obama for talks in Washington on Monday.

Boko Haram controlled territory around the size of Belgium at the end of 2014. Nigeria has managed to push the militants out of most of that with the help of troops from neighboring Chad, Niger and Cameroon.

However, the militants have dispersed and in recent weeks have carried out a string of attacks on targets in northern Nigeria and the countries with which it shares borders.