The IS extremists in 2014 launched their self-proclaimed "caliphate" across swathes of both countries in a campaign marked by its brutality including mass killings, torture, rape and slavery.

US-backed counter-offensives ended their territorial hold in Iraq in 2017 and in Syria in 2019, but IS cells continue to target security forces and civilians in both countries.

"Since the beginning of this year in Iraq... through the first week of April, we have seen a record of a 68-percent reduction in attacks when compared to the same period last year," said US Major General Matthew McFarlane, commander of the anti-jihadist coalition.

"In Syria... we recorded a 55-percent decrease during the same time," McFarlane told an online news conference.

The attacks attributed to IS fighters this year have been "relatively small, from one to a few individuals", he said, adding the group "has failed to organise or coordinate anything more than that over the past year".

The Muslim fasting month of Ramadan, which ended last week, was "one of the most peaceful in years", the general said, noting an "80-percent decrease from last year" in Iraq and 37 percent for Syria.

Since February, a string of IS attacks targeting truffle hunters in Syria and landmines left by the extremists have killed at least 240 people, according to the Britain-based monitor Syrian Observatory for Human Rights.

McFarlane also said "over 1,300 third-country nationals" had been repatriated from the Kurdish-administerd Al-Hol camp in northwest Syria, which is home to about 50,000 people including family members of suspected jihadists.

Last month an Iraqi general said IS still had up to 500 active fighters in the country, now based in remote desert and mountain hideouts.

The United Nations estimated in a report published in February that IS still has "5,000 to 7,000 members and supporters" across Iraq and neighbouring Syria, "roughly half of whom are fighters".

In Iraq, IS cells operate in rural mountain areas, "leveraging the porous Iraqi-Syrian border and retaining manoeuvrability to evade attacks" while trying to "rebuild and recover", the UN report said.

The report estimated IS's "dwindling cash reserves" at $25 million to $50 million and said it had started investing in hotels and real estate to launder money and engaging in cattle rustling to raise funds.