On Thursday evening US officials confirmed the military had used the largest non-nuclear weapon in its arsenal for the first time ever in a strike against a suspected jihadi stronghold.
The MOAB was dropped over Afghanistan's Nangarhar province where ISIS is believed to have a network of tunnels.
Mr Stoltenberg said: “Nato’s core task is to defend Nato allied countries, the 28 European countries, and the United States and Canada.
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US President Donald Trump has the support of his Nato allies, Jens Stoltenberg said
“We are addressing the root causes of the terrorist threats we see against many Nato allied countries. We are in Afghanistan to fight international terrorism.
“The main reason for Nato being there for so many years is to prevent Afghanistan from becoming a safe haven for international terrorists once again. We are in Iraq training Iraqi forces, enabling them to stabilise their own country and to fight terrorism, to fight [ISIS] in Iraq.
"Nato is supporting the US-led coalition fighting [ISIS] in Syria with our surveillance planes helping to improve the air picture.
“All Nato allies are a part of the coalition, some of them are active on the ground Syria. So Nato and Nato allies participate and contribute in many different ways to the international fight against terrorism.”
The former Norwegian prime minister also said he welcomed Donald Trump’s change of heart after he branded Nato “obsolete” during the Presidential election campaign.
Nato is supporting the US-led coalition fighting [ISIS] in Syria
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Mr Stoltenberg suggested looking to the past was proof enough that a strong Nato was as important for North America as it is for Europe.
“I very much welcome the strong commitment of President Trump and his security team to Nato,” he said.
“A strong Nato is important for Europe but it’s also important for the United States. Two World Wars and a Cold War taught that peace and stability in Europe is also important for the security and prosperity of North America.
“We have to remember the only time Nato has invoked our collective defence clause, Article 5, was after an attack on the United States on 9/11. So Nato is important for North America and for Europe but we have to adapt, we have to change.
“And I agree with President Trump that we have to step up our efforts to fight international terrorism and we need fairer burden sharing, meaning that many allies have to invest more in defence.”
11 things you need to know about NATO
Tue, February 14, 2017
NATO – The North Atlantic Treaty Organization is an intergovernmental military alliance based on the North Atlantic Treaty which was signed on 4th April 1949. The organization constitutes a system of collective defence whereby its member states agree to mutual defence in response to an attack by any external party.
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Every member country, no matter how large or small, has an equal say in discussions and decisions. Photo shows: Signing the North Atlantic Treaty which marked the beginning of NATO, 1949.
President Trump meet with the Nato chief on Wednesday and during a joint press conference, he said: “I said it was obsolete. It’s no longer obsolete.”
The US contributes around 70 per cent of Nato’s total defence spending and while president Trump conceded that the alliance was still “very important” to him, the Republican blasted other members that do not contribute enough.
Mr Trump added: “If other countries pay their fair share instead of relying on the United States to make up the difference, we will all be much more secure, and our partnership will be made that much stronger.
“The secretary general and I had a productive discussion about what more Nato can do in the fight against terrorism.
“I complained about that a long time ago and they made a change, and now they do fight terrorism.”