WASHINGTON (REUTERS) - The killing of Islamic State leader Abu Bakr al-Baghdadi in a US raid is a further blow to a jihadist group that once held a swathe of territory in Iraq and Syria, experts said, but the organisation and its ideology remain dangerous.
Where once they confronted armies, the extremist Islamist group's adherents have in recent years staged hit-and-run and suicide attacks. In some cases, the group has claimed responsibility for atrocities such as bombings in Sri Lanka in April that killed more than 250 people.
Islamic State's involvement is not always proven, but even if the link is ideological rather than operational, it is still seen as a security threat in many countries.
After defeat by US-backed forces, Islamic State has reverted to the guerrilla tactics it was once known for.
Iraqi security forces routinely carry out operations against remnants of the Jihadist group, more than two years after its defeat.
Sleeper cells have regrouped in provinces including Diyala, Salahuddin, Anbar, Kirkuk and Nineveh, where they have carried out frequent attacks, including kidnappings and bombings aimed at undermining the Baghdad government.
Although cells operate mostly in rural areas, burning crops and extorting local farmers, in February, two people were killed and 24 wounded when a car bomb went off in Mosul, once the group's capital in Iraq.
The Pentagon said in January that IS was regenerating faster in Iraq than in Syria. Analysts estimated earlier this year that about 2,000 active combatants now operate in Iraq.
After serious military setbacks, Islamic State slipped into the shadows, staging suicide bombings and ambushes. It has carried out bomb attacks in towns and cities in northern Syria in the past year, including targeting US forces.
Syrian Kurdish forces, who crushed the jihadists across the north and east with US help, have said they believe sleeper cells mushroomed in eastern Syria. They have warned of the risk posed by holding thousands of militants in prisons, including foreigners from around the world.
That warning came into sharp focus this month when US President Donald Trump announced he was withdrawing US troops from northeastern Syria, opening the way for Turkey to launch an offensive targetting Kurdish fighters near its border.
Turkey says it has captured some 200 IS detainees who fled prisons in the area of its offensive and has transferred them to other prisons under the control of Turkish forces and its Syrian rebel allies. President Tayyip Erdogan has said any IS prisoners will be brought to justice.
Islamic State fighters still hold some ground in Syria's remote central desert in territory otherwise held by the Damascus government.
Egypt has seen no large attacks over the past year, but smaller incidents persist and the military is mounting a campaign against Islamist insurgents, mainly on the Sinai Peninsula.
The military says several hundred militants have been killed since it launched a major campaign in February 2018 to defeat fighters linked to Islamic State in Sinai.
A Russian passenger jet was bombed shortly after takeoff from the Egyptian resort of Sharm el-Sheikh in 2015, killing all 224 people on board. The attack was claimed by Islamic State.
Islamic State militants have carried out deadly bombings and shootings in Saudi Arabia against security forces and minority Shi'ite Muslims, after the authorities crushed an Al Qaeda insurgency more than a decade ago.
Baghdadi called for attacks against Saudi Arabia when the kingdom joined the US-led coalition in mounting air strikes against his group. In his speeches, he also used derogatory terms when he referred to the rulers in Riyadh.
Kamran Bokhari, a director at Washington-based think-tank the Centre for Global Policy, said earlier this year that Islamic State exists in the kingdom but Saudi security forces and intelligence service are "pretty much on top of things" YEMEN Islamic State militants announced a Yemeni affiliate in late 2014 as the country descended into civil war between the Saudi-backed government of Abd-Rabbu Mansour Hadi and the Iran-aligned Houthi movement.
However, the group has since faced tough resistance from Al Qaeda's local branch, Al Qaeda in the Arabian Peninsula (AQAP), and both groups fought each other, especially in the southern province of al-Bayda. Al Qaeda and Islamic State are also fighting Shi'ite Houthis, which they see as heretics.
Islamic State has claimed several assassinations and bombings in south Yemen but has never held territory. Experts believe Al Qaeda, with older and deeper tribal connections, poses a bigger threat in the war-torn country.
Nigerian group Boko Haram has carried out attacks in northeastern Nigeria since 2009 in pursuit of an Islamic caliphate. It has killed more than 30,000 people and forced 2 million to flee their homes. The group split in 2016 and one faction pledged allegiance to IS.
Islamic State's West Africa Province (ISWAP) has focused on attacking military bases in raids over the last year. It has become the dominant militant group in the region.
The extent of support provided by Islamic State to ISWAP is unclear and many security experts say the relationship is mainly in name rather than direct funding and logistical support.
Islamic State in Khorasan (ISIS-K), which took its name from a historical region that covered much of modern-day Afghanistan and parts of Central Asia, appeared in late 2014 in the eastern province of Nangarhar, where it retains a stronghold. It announced its formation in January 2015.
The group's leadership has pledged allegiance to Baghdadi but it is not clear that ISIS-K has direct operational links with the main movement.
It has claimed attacks on civilian targets in cities including Kabul and fought the Afghan Taleban for control of a number of rural districts. US commanders say its forces number fewer than 2,000.
The movement is little understood and many Afghan officials in Kabul doubt the veracity of some of its claims of responsibility.
Islamic State claimed the Easter Sunday bomb attacks on churches and hotels in April and released a video showing eight men declaring loyalty to Baghdadi.
IS claimed the men in the video, released by its Amaq news agency, carried out the suicide bombings.
Sri Lankan officials blamed two domestic Islamist groups with suspected ties to Islamic State.
Indonesia is the world's most populous Muslim-majority country and most people practise a moderate form of Islam. But there has been a resurgence in militancy and authorities have said they believe thousands of Indonesians draw inspiration from Islamic State, while about 500 Indonesians are thought to have gone to Syria to join the group. A court sentenced a cleric, Aman Abdurrahman, to death last year for masterminding deadly attacks. Abdurrahman is considered the ideological leader of Jemaah Ansharut Daulah (JAD) - a loose grouping of Islamic State sympathisers in Indonesia.
Suicide bombings in May last year in Surabaya that killed more than 30 people were linked to JAD cells.
The Philippines fears that extremists fleeing Iraq and Syria could find a safe haven in the jungles and remote villages of Muslim areas of Mindanao, where there is a long history of lawlessness, clan rivalry and separatist and Islamist rebellion.
Several splinters of the myriad armed groups in the southern Philippines have pledged allegiance to Islamic State, although none are known to have been endorsed as its Southeast Asian affiliate.
Islamic State has often claimed responsibility for bombings and rebel clashes with government troops in Mindanao, but their veracity is often disputed.