The Afghan military has launched a major offensive against the Islamic State group in the country's far eastern region near the border with Pakistan, after a massive attack on Kabul.
The offensive began over the weekend in Nangarhar province, where IS has had a presence for the past year, said Dawlat Waziri, spokesman for the Defence Ministry.
The offensive, part of the government's Operation Shafaq - or Dawn in Pahsto - started hours after an IS suicide bomber killed at least 80 people who were taking part in a peaceful demonstration in Kabul on Saturday.
It was the deadliest attack to hit the Afghan capital since the 2001 US-led invasion.
President Ashraf Ghani gave the orders for the offensive, which Mr Waziri said will consist of air strikes and ground attacks, including those by special forces.
Clean-up operations aimed at ensuring that IS loyalists do not return to the area would follow, he added.
The offensive marks a new chapter in Afghanistan's war against insurgents. Until now they have been a largely defensive force, and have struggled to take the lead on the battlefield since the withdrawal in 2014 of most international combat forces.
The head of US and Nato forces in Afghanistan, General John Nicholson, has pledged to transform the Afghan military into an offensive force so they can take the fight to the insurgents, and reclaim battlefield initiative.
The main fight is against the Taliban who have been battling to overthrow the Kabul government for 15 years.
But this counter-terrorism operation against the IS group will enable General Nicholson to implement an aggressive new strategy, working closely with the Afghan military and using more air strikes against the enemy, said analysts.
US President Barack Obama recently expanded the conditions for US troops in Afghanistan to support Afghan offensive operations.
General Nicholson can make the strategic shift from using air power only to defend US and Nato positions, to striking in support of Afghan offensives.
President Obama's directives, issued in June, enable the US military to work alongside Afghan forces in the field on offensive missions against insurgents, though still in a non-combat role.
Since 2014, their role was confined to battles in which the Taliban directly threatened US and Nato.
They also allow US involvement when Afghan forces face "strategic defeat," as they did in the northern provincial capital of Kunduz, which briefly fell to the Taliban last September and was threatened again in April.
The US military spokesman in Kabul, Brigadier General Charles Cleveland, said American forces have been involved in the current operation in the east and are conducting "multiple counter-terrorism strikes."
He said that since January 1, US forces conducted "more than 450 kinetic strikes" both under the new authorities and for force protection.
Haqiqullah Walizada, spokesman for the fourth regiment of the Afghan army's 201 Corps, said 260 IS gunmen had been killed in the Kot and Achin districts since the offensive began.
Another 122 had been wounded, he said.
Mr Walizada said that Kot, which shares a border with Pakistan, was the main IS stronghold in the region.
"During the operation a large number of IS fighters were killed, including the recently-appointed group commander Saeed Emarati," he said.
Emarati was a Taliban fighter but swapped allegiance after it was revealed last year that the founder and then-leader of the Taliban, Mullah Mohammad Omar had been dead for more than two years, said Mr Walizada.
The formal start of the US-backed offensive in Nangarhar appears to be an extension of months of attacks on IS positions in the region. Afghan authorities have claimed huge numbers of IS loyalists killed in these operations, though without details or verification.
Officials have said that IS loyalists in Afghanistan are mostly former fighters for the Taliban or other insurgent groups including the Pakistani Taliban known as Tehrik-i-Taliban or TTP.
Elsewhere in the country, Taliban gunmen attacked police checkpoints in Uruzgan province, in the south, where they have been active for many months.
The director of the Uruzgan provincial council, Abdul Kareem Khadimzai, said the militants launched their attack on checkpoints on the strategic Kandahar-to-Uruzgan highway, killing three policemen and taking five others hostage.