The announcement was made at a ministerial meeting of the international coalition against IS in Riyadh, which was co-hosted by Saudi Arabia and the United States with the aim of raising $601 million for a stabilisation fund.

"I'm announcing that the United States is committing $148.7 million to that fund," said US Secretary of State Antony Blinken, who kicked-off a three-day visit to Saudi Arabia on Tuesday.

"This support will meet critical needs that Syrians and Iraqis themselves have identified."

Saudi Foreign Minister Prince Faisal bin Farhan said it was "disheartening and absolutely unacceptable" that some wealthy countries had not repatriated citizens who had travelled to Iraq and Syria to join IS.

"To those countries, you must step up, you must take your responsibility," said the top diplomat who held separate talks with French Foreign Minister Catherine Colonna on the sidelines of the coalition meeting.

Colonna is expected in Doha later Thursday for a strategic dialogue session.

The "caliphate", which IS proclaimed across swathes of Iraq and Syria in 2014, was declared defeated in 2019 following counter-offensives in both Iraq and Syria.

Thousands of jihadists and their family members continue to be held in detention centres and informal camps where US commanders have warned they could fuel an IS revival.

- 'Take up arms' -

Despite repeated calls for their repatriation, foreign governments have allowed only a trickle to return home, fearing security threats and domestic political backlash.

Blinken applauded countries that have brought home their nationals from Syria, urging other nations to follow suit.

"Repatriation is critical" to reduce populations of large informal camps such as Syria's Al-Hol, which houses 10,000 foreigners, including IS relatives, he said.

"Failure to repatriate foreign terrorist fighters risks the possibility that they could again take up arms and attempt to restore" the IS proto-state, he added.

The anti-IS coalition was formed in 2014 following the jihadists' lightning advance that saw reports of atrocities multiply as they overran non-Muslim as well as Muslim areas.

Despite its territorial defeat, IS militants continue to conduct attacks against civilians and security forces in both Iraq and Syria.

The United Nations estimates that IS still has 5,000 to 7,000 loyalists across the two countries, roughly half of whom are fighters.

Fellow coalition member Britain will pledge more than $109 million over the next five years to support stabilisation efforts in Iraq and Kurdish-controlled northeastern Syria, its foreign ministry said.

This comes on top of $19.9 million in aid over the next two years to specifically address acute humanitarian needs in northeastern Syria, it added.

- US partnership -

Thursday's coalition meeting came a day after Blinken told diplomats from Gulf Cooperation Council countries that the US remains "deeply invested" in Gulf partnerships.

The US secretary of state flew into Saudi Arabia on Tuesday, kickstarting a visit aimed at boosting ties with its longtime ally, which has begun forging closer relations with Washington's rivals.

Relations with Riyadh have been strained in recent times, mainly over human rights and oil, after US pleas for help in bringing down skyrocketing prices last year were dismissed.

The three-day visit is Blinken's first since the kingdom restored diplomatic ties with Iran, which the West considers a pariah over its contested nuclear activities and involvement in regional conflicts.

On Tuesday, the day Blinken arrived, Iran reopened its embassy in Riyadh after a seven-year closure, with Iranian Deputy Foreign Minister Alireza Bigdeli hailing a "new era" in ties.

On the same day, the kingdom's de facto ruler, Crown Prince Mohammed bin Salman, hosted Venezuelan President Nicolas Maduro, the head of a fellow oil power which has long sparred with Washington.

On Wednesday, a day after meeting Blinken, Prince Mohammed received a phone call from Russian President Vladimir Putin.

"Particular attention was paid to measures aimed at strengthening trade and economic ties," according to a statement released by Russian state media.

"Preserving the stability of the global energy market was discussed extensively."