Nigerian teachers went on strike and staged rallies nationwide on Thursday in protest against the kidnapping of more than 200 schoolgirls by the Islamist Boko Haram sect and the killing of nearly as many teachers during its insurgency.

Boko Haram gunmen stormed a school outside the remote northeastern town of Chibok on April 14, carting some 270 girls away in trucks. More than 50 have since escaped but at least 200 remain in captivity, as do scores of other girls kidnapped previously.

National Union of Teachers (NUT) President Micheal Alogba Olukoya told reporters Boko Haram, whose name means “Western education is sinful,” had killed 173 teachers over five years.

In Maiduguri, capital of the northeastern state of Borno where the insurgency is most intense, around 40 teachers marched down a street past rows of cicada trees to the office of Governor Kashim Shettima chanting “bring back our girls” and holding placards saying “vulnerable schools should be fenced”.

Shettima came to the gates of the compound to meet the teachers, who were clothed in black union vests over their long, flowing traditional robes and were escorted by the military.

President Goodluck Jonathan and the military have come under intense criticism for their slow reaction to the mass abduction, although last week Nigeria accepted help from the United States, Britain, France and China to help find the girls.

The United States has deployed about 80 military personnel to Chad in its effort to help find the girls, President Barack Obama told Congress on Wednesday.

Boko Haram has threatened to sell the girls into slavery but has also offered to swap them for jailed militants.

“All schools nationwide shall be closed as the day will be our day of protest against the abduction of the Chibok female students and the heartless murder of the 173 teachers,” NUT President Micheal Alogba Olukoya told reporters.

Boko Haram wants to create a breakaway Islamic state in a religiously-mixed, Muslim and Christian country of 170 million people, Africa’s most populous. Its militants have attacked hundreds of school, killing hundreds of teachers and students.

No teachers were killed in the Chibok attack.

“We remain resolute in our resolve to continue the campaign even as we mourn the death of our colleagues until our girls are brought back safe and alive and the perpetrators of the heinous crime are brought to book,” Olukoya said.

In Lagos, Nigeria’s commercial metropolis and port of 21 million people in the south, around 350 teachers gathered in the green Gani Fawehinmi park. One carried a placard reading: “You can’t intimidate us.”

“Children’s lives are being threatened, kidnapping all over the place, stealing, maiming of life, that’s what we are saying should stop,” teacher Ojo Veronica told Reuters Television.

The Boko Haram insurgency has killed an estimated 5,000 people since an initial uprising in 2009.

The Chibok kidnapping has drawn international attention to Nigeria and Boko Haram, much of it driven by the #BringBackOurGirls Twitter campaign, which has been supported by celebrities like Michelle Obama and film star Angelina Jolie.