The operation is understood to relate to a possible plot involving Islamist extremists with potential targets in the UK.
The threat was not thought to be imminent.
Some of those arrested are understood to be British nationals.
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A post-mortem report found no traces of drugs or alcohol, and the evidence suggests Simon Brown was not taking photos.
The masked men used an angle grinder to tear through the lock.
Doing as little as possible in the first minute helps people regain control of breathing and increases chances of survival, says the RNLI.