European governments have moved to their highest levels of alert for years following the attack last week on a concert hall in Moscow by militants from IS, which killed 140 people.
Within 48 hours, France increased its surveillance and risk warning to the highest level and Italy ordered enhanced measures. In Germany, officials described an "acute risk".
The attack in Moscow, the most lethal Islamist extremist operation in Europe, was claimed by IS, which officials believe has been planning new operations against European targets for several years.
Between 2015 and 2019, when IS ran a so-called caliphate across a swath of land it controlled across eastern Syria and western Iraq, the group's central leadership had little need of its newly established affiliates to launch operations in Europe as it had all resources to hand with foreign recruits, money and training camps.
This led to series of lethal attacks in France and Belgium.
However, years of counterterrorism operations by local security forces, the US and others, have degraded IS in its former strongholds and the group is fragmented and weak.
Western security officials with close knowledge of IS in Iraq and Syria said the group had abandoned its project of rebuilding the so-called caliphate but that successful strikes at international targets were seen as "good for morale and the IS brand and compensate for failure closer to home".
Recent US-led counter-terrorist operations have killed a series of IS leaders in Syria who were thought to have been planning terrorist attacks in Europe.
Analysts at the Washington Institute, a US-based thinktank, wrote: "[The US military's] decision to act against these individuals may indicate that the threat they posed needed to be dealt with immediately.
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