Militants have killed at least 73 soldiers in an attack on a military base in western Niger - the deadliest in several years.Twelve soldiers were also injured in the attack in Inates, the army says.No group has said it was behind the killings.But militants linked to al-Qaeda and Islamic State have staged deadly attacks across the Sahel region this year despite the presence of thousands of regional and foreign troops.Security analysts say the insurgency in Niger is escalating at an alarming rate.Niger's defence minister, Issoufou Katambe, told the BBC "a large number of terrorists" had been "neutralised".Mr Katambe told the BBC that there had been "a fierce battle" with "several hundred" militants in Inates near the border with Mali.The attack came days ahead of a planned summit in France, where President Emmanuel Macron and five West African leaders were due to discuss security in the region.But Mr Macron, along with Niger's President Mahamadou Issoufou, has now said the summit would be postponed to early next year.Niger's government earlier requested a three-month extension to a state of emergency, which was declared two years ago. Niger's army is struggling to contain the spread of armed groups.In recent weeks, there have been increasingly bold attacks by militants liked to the Islamic State group in the area of the country close to Mali.Insurgents are active across the region and Niger is a member of the G5 Sahel group - along with Burkina Faso, Mali, Mauritania and Chad - which aims to fight the militants. French soldiers are deployed in the Sahel to support this effort.Last month, 13 French soldiers died in Mali when two helicopters collided during an operation against jihadists there.