OUAGADOUGOU (Reuters) - Burkina Faso’s army said it had killed nearly 150 militants in response to an attack on civilians this week, but an international rights group said some of them had been executed in front of their families.

The army has stepped up operations in response to worsening security across northern Burkina since last year, including attacks by Islamist militants and inter-ethnic clashes, leading to accusations of extrajudicial killings and arbitrary arrests.

Rights activists fear such abuses could fuel spiralling instability in previously peaceful Burkina as they have in neighbouring Mali, where jihadist groups have tapped into ethnic rivalries and anger with the central government to recruit.

The violence in the West Africa’s Sahel region, a semi-arid band below the Sahara, has alarmed former colonial power France and the United States, who have deployed thousands of troops to the zone to counter al Qaeda and Islamic State-linked groups.

Burkina’s government and army spokesmen could not immediately be reached for comment on Wednesday. The government has acknowledged some abuses in the past and pledged to take action.

In the latest incident, militants killed 14 civilians on Monday near the Mali border, the army said. Subsequent ground and air operations “neutralised 146 terrorists”, army spokesman Lamoussa Fofana said in a statement.

But Corinne Dufka, West Africa director for New York-based Human Rights Watch (HRW), said on Wednesday that some of the so-called terrorists were executed in front of the families, according to sources HRW had interviewed.

“Security forces have suffered serious losses over the last six months,” she told Reuters on Wednesday by telephone. “(But) they are engaging in alleged reprisals against the civilian population.”

Dufka added that HRW had documented 30 jihadist attacks in recent weeks, and said the group would soon publish a full report on atrocities by both sides.

Burkina declared a state of emergency in several provinces in December following an attack by an al Qaeda-linked group. The state of emergency was extended by six months in January after an outbreak of ethnic violence killed dozens.

Thousands of people have fled their homes as a result of militant attacks and reprisals by the Burkinabe army, HRW said in a report last May.