"The Islamic Emirate is going to launch the spring operations under the inspirational name of 'Azm' (Determination) at 5 am on 24th April 2015," the Taliban said in a statement on Wednesday, using the group’s official name.
"The main targets of these operations… will be the foreign occupiers, especially their permanent military bases… officials of the stooge regime, their military constellations, especially their intelligence, interior ministry and defence ministry officials."
This year’s attacks are expected to be the bloodiest in a decade as NATO forces pull back from the frontlines, leaving Afghan forces to battle insurgents without the full support of US-led foreign combat troops for the first time.
The Islamist militant group has been fighting the Afghan government and its foreign backers since it was ousted from power in 2001.
"If the foreign occupiers really want to relieve themselves from this nuisance of fighting, they should immediately withdraw," the Taliban said in the statement.
"The Islamic Emirate is going to launch the spring operations under the inspirational name of 'Azm' (Determination) at 5 am on 24th April 2015." — A statement from the Afghan Taliban
While NATO's combat mission formally ended in December, a small follow-up foreign force has stayed on to train and support local security personnel.
In March, US President Barack Obama backpedalled on plans to shrink the US force in Afghanistan this year by nearly half, agreeing to keep the current level of 9,800 American troops until the end of 2015.
An Afghan defense ministry spokesman dismissed the Taliban announcement, saying the armed forces were ready to battle any insurgent offensive.
"Our enemies don't have the capability to collapse any province or district," Brigadier General Dawlat Waziri was quoted as saying by Reuters.
More than more than 10,000 Afghan civilians were killed or injured in the conflict in 2014, which was the worst year for civilians there since the United Nations began keeping records in 2009.
In the first three months of 2015, civilian casualties from ground fighting were up 8% from the same period last year, according to a copy of UN report obtained by Agence France-Presse.
But in their statement, the Taliban said their "top priority will be given to safeguard and protect the lives and properties of the civilian people" during the offensive.
— Resolute Support (@ResoluteSupport) April 22, 2015
Resolute Support, the name for the NATO mission in Afghanistan, responded on Twitter: "Taliban should seek peace through political process instead of putting more innocent Afghan civilians at risk."