Islamic State conflict: 10,000 militants killed in nine months - US
More than 10,000 Islamic State fighters have been killed since an international coalition began a campaign against the group in Iraq and Syria, the US says.
Deputy Secretary of State Antony Blinken told France Inter radio the coalition had seen "a lot of losses" within IS in the past nine months.
"It will end up having an impact," he added, but warned IS remained resilient and capable of taking the initiative.
He spoke after the coalition met in Paris to discuss its strategy in Iraq.
Representatives backed Iraqi Prime Minister Haider al-Abadi's plan to retake the city of Ramadi, whose capture by IS last month he described as a "failure" for the international community.
They also called for the "speedy launch" of efforts to end the conflict in Syria.
Suicide truck bombings
In his interview with France Inter on Wednesday, Mr Blinken insisted that the coalition campaign had not been a failure.
"There has been important progress, but equally Daesh remains very resilient and capable of taking the initiative," he said, using a pejorative term for the group based on the Arabic acronym of its former name.
Mr Blinken said IS now controlled 25% less territory in Iraq than it did when coalition air strikes began in August 2014, and that it had lost significant numbers of men and materiel.
But he also acknowledged recent setbacks, including the loss of Ramadi, where Iraqi soldiers fled their positions despite vastly outnumbering the IS force attacking them.
"At the start of this campaign [we] said it would take time," he said. "We have conceived a three-year plan and we're nine months into it."
Mr Blinken's assertion that more than 10,000 IS fighters had been killed could not be independently verified.
The UK-based Syrian Observatory for Human Rights reported at the end of April that coalition air strikes in Syria had left more than 1,922 IS fighters dead, along with 66 civilians.
In February, the US Director for National Intelligence James Clapper told Congress that IS could muster "somewhere in the range between 20,000 and 32,000 fighters", but that there had been "substantial attrition" in its ranks.
Separately on Wednesday, the Iraqi ambassador to France, Fareed Yasseen, welcomed the US decision to send 2,000 AT-4 missiles for use against armoured suicide truck bombs, which helped weaken and demoralise government forces in Ramadi.
"The French will be giving us similar weapons, ammunition and we are discussing other co-operation projects," he told Europe 1 radio.
On Tuesday, explosives-laden armoured vehicles were used in four suicide attacks in south-west of Baiji in Salahuddin province which targeted security forces personnel and members of the Popular Mobilisation, a volunteer force of mostly Shia militias, a security source told the BBC.
The source said 28 militiamen were killed and 36 others wounded in the bombings.
On Tuesday, Iraq's prime minister urged the coalition to give his government more support, including by allowing it to obtain weapons from sanctions-hit Iran and Russia.
"Armament and ammunition, we haven't seen much. Almost none. We're relying on ourselves, but fighting is very hard this way,'' Mr Abadi told reporters before the Paris meeting.