Niger has declared three days of mourning after a deadly attack blamed on Boko Haram terrorists left 30 Nigerien soldiers dead. The troops clashed with the militants in the town of Bosso, on the border with Nigeria, on Friday ( 3 June) night.

Two Nigerian soldiers are also believed to have been killed. It was the deadliest attack in Niger since April 2015, when at least 74 people, including 28 civilians, were killed at Lake Chad's Karamga island.

Boko Haram captured Bosso , but Nigerian troops regained control of the town. Bosso's mayor, however, claimed the town was recaptured by the militants on 6 June, Reuters reported. The Nigerien government denied the take-over and claimed the town was "completely under control".

Who are Nigeria's Boko Haram terrorists?

Boko Haram, which has renamed itself Iswap, fights against Western influence in Nigeria and aims to impose its version of Sharia law throughout occupied territories.

The militants launch attacks in Nigeria and neighbouring countries in a bid to take control of more territory. Three Nigerian states − Adamawa, Borno and Yobe − have been under a state of emergency since May 2013.

Boko Haram has killed more than 20,000 people since 2009 and was deemed the world's deadliest terror group, surpassing its ally, Islamic State (Isis/Daesh), in November 2015. Nigeria has become the world's third most terrorised country as a result of the group's violent insurgency.

Read more about Boko Haram

Boko Haram primarily targets north-eastern Nigeria, but attacks also occur in neighbouring nations and other parts of Nigeria. Bosso is part of the Diffa region, often targeted by Boko Haram. In 2015, both Chad and Niger declared a state of emergency in areas affected by attacks blamed on the Islamist rebels.

At least 50,000 people have fled Bosso since 3 June, from estimates by the UN High Commissioner For Refugees (UNHCR). "Many people are traumatised and worried about their safety. People are sleeping in the open and urgently need shelter and other assistance," the agency said in a statement.

"The welfare of these people and others forced to flee the violence in Bosso is of great concern. Insecurity and lack of access have long hampered humanitarian operations in parts of the Diffa region."

Regional offensive

Niger is part of an ongoing regional offensive against the terrorists. The task force consists of 8,700 troops from Nigeria, Niger, Chad, Cameroon and Benin and has scored some success, such as the recapture of several territories and the release of thousands of civilians held captive.

Although Nigeria's President Muhammadu Buhari declared a technical victory over the insurgents in December 2015, Boko Haram has continued to carry out attacks, with security experts warning underlying issues such as disenfranchisement, poverty and strong links with IS are still major threats to stability in the region.

A picture taken on 25 May 2015 shows a sign proclaiming: 'No future for Boko Haram, long live Niger' in a market in the south-eastern city of Bosso, near the border with Nigeria, in Diffa region Getty Images