Resolute Support Commander, Gen John W Nicholson, said during a visit to the northern province of Kunduz that Mansour rejected the chance offered by Afghan President Ashraf Ghani to participate in the peace process.
"I hope that the Taliban leadership will realize it is time to lay down their weapons and join the peace efforts, so the people of Afghanistan can enjoy peace and prosperity in the future," Nicholson said.
Nicholson was in Kunduz for the second time since becoming commander of the Resolute Support mission. In late September 2015, Mansour's Taliban fighters overran the city of Kunduz and held it for four days before being driven out. The takeover was a major embarrassment for Ghani's government.
Nicholson also met victims and families of people killed on October 3, 2015 when US warplanes mistakenly bombed a Kunduz hospital run by Doctors Without Borders during the offensive to retake Kunduz.
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The hospital was destroyed and 42 people killed in the attack, which the Pentagon said was a mistake caused by human error.
Mansour, believed to be in his 50s, was killed when a US drone fired on his vehicle in the southwestern Pakistani province of Baluchistan. He had emerged as the successor to Taliban founder Mullah Mohammad Omar, whose 2013 death was only revealed last summer.
Today, Pakistan's Prime Minister on Foreign Affairs summoned US Ambassador David Hale to "express concern over the drone strike on Pakistani territory," which it views as a violation of the country's sovereignty, according to a foreign ministry statement.
"This year will be the year of destruction and defeat for the Taliban, as they lost their leader. This will make them weak in all parts of the country and finally this terrorist group will be destroyed," Sediqqi said.