* Military has stepped up offensive against Boko Haram
* State of emergency extended last week
Nigeria's military said on Friday that it may have killed more than 50 Islamist insurgents in an airstrike on one of their main bases in the northeast of the country.
The latest strikes on Thursday targeted Boko Haram sect hideouts in the Gwoza hills, near the border with Cameroon.
In May, the military stepped up an offensive against the Islamist group, which is fighting to establish an Islamic state in Nigeria, Africa's most populous country split roughly evenly between Christians and Muslims. President Jonathan declared a state of emergency and ordered in extra troops.
"We had intelligence that Boko Haram were still hiding somewhere around the Bita bush. Some villagers alerted us," Colonel Muhammad Dole, spokesman for Nigerian forces in the northeast, told Reuters.
"We may even have killed more than that 51 because the pilot didn't capture the images at that time. Our troops are on ground in the area now," he added, declining to give details of the aircraft used.
The military often reports large death tolls among Islamists in fighting but rarely acknowledges significant casualties on its side. It is usually impossible to verify the casualty figures.
The House of Representatives, the lower chamber of Nigeria's federal parliament, last week approved a six-month extension of a state of emergency in areas where the offensive is going on.
Initially, Jonathan's military campaign tempered violence as soldiers wrested back control of towns, cities and stretches of semi-desert in the northeast.
But the insurgents have proved resilient. Boko Haram fighters retreated into semi-arid land near the northern border with Niger and steep forested hills near Cameroon, from where they have mounted deadly counter-attacks and have intensified killings of civilians.