Prime Minister Haider al-Abadi, speaking in London at a meeting of the international coalition, also warned of the impact of falling oil prices on his country's ability to defeat IS.
"We don't want to see a military defeat because of budget and fiscal problems," Prime Minister Haider al-Abadi told reporters after talks with US Secretary of State John Kerry and ministers from 19 other countries in London.
The United States assembled a coalition of about 60 countries last year, including Arab nations, to take action against the Islamist group after it seized a swathe of territory in Iraq and Syria.
Coalition members have conducted almost 2,000 air strikes against IS targets in the past four months, killing "thousands" of its fighters -- including "50 percent of the top command", Kerry said.
"They have definitively put Daesh on the defensive where those strikes take place and in that particular region," he said, referring to the IS group by its Arabic acronym.
But Iraq's security forces are on the frontline of the ground battle and they are struggling.
The former head of Britain's MI6 secret intelligence service, John Sawers, said this week that an attack in the UK was now "highly likely" due to a "hardened core" of militants returning home from fighting in Syria and Iraq.
Abadi, who before the meeting had talks with Prime Minister David Cameron in Downing Street, said there had been a recent increase in the delivery of weapons to his security forces, and reported a positive response at Thursday's talks to a request to defer payment.
But he warned that the 60-percent fall in world oil prices since June had been "disastrous" for his country, where 90 percent of the budget is dependent on oil.
"Iraq needs weapons -– and the international community has the ability to provide Iraq with the weapons it needs," Abadi said at a press conference flanked by Kerry and British Foreign Secretary Philip Hammond.
Both foreign ministers promised to supply what Iraq needed, saying the London meeting was intended to take stock of progress so far and establish what more action was needed.
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"We've heard very clearly what he said," Hammond said. "This campaign is not going to fail for want of some guns or some bullets in the hands of the Iraqi security forces."
Kerry added that the IS group "is not simply a Syrian problem, it's not an Iraqi problem -- Daesh is global problem".
'CHALLENGE OF OUR TIME'
The meeting was the second held by the coalition but unlike December's talks in Brussels, only core members were invited.
It was their first chance to discuss as a group this month's attacks in Paris against the satirical magazine Charlie Hebdo and a Jewish supermarket, which left 17 people dead and were claimed by Al-Qaeda in Yemen and the IS group.
Looming over the meeting was also the Friday deadline imposed by IS militants threatening to kill two Japanese nationals unless they are paid a $200 million ransom.
"Terrorists want to drive us apart, but in fact their actions have had the opposite effect, they're bringing us together," Kerry said ahead of the meeting at the lavish 19th century Lancaster House in central London.
Asked about the Paris attacks, and terror raids in Belgium last week, the US diplomat said the public should take heart.
"In a sense we are flushing them out. These sleeper cells have been there for years now," he said, adding that they represented "the challenge of our time".
The coalition will set up expert-level groups to address specific issues relating to the IS group, from stopping the flow of foreign fighters that swell its ranks to cutting off sources of funding and their resources.
"Faced with such a threat, it is important to have a comprehensive, coherent strategy, and political leadership," French Foreign Minister Laurent Fabius said.
Thursday's talks were attended by Australia, Bahrain, Belgium, Canada, Denmark, Egypt, France, Germany, Iraq, Italy, Jordan, Kuwait, the Netherlands, Norway, Qatar, Saudi Arabia, Spain, Turkey and the United Arab Emirates.