An NCA spokesman said: “West Yorkshire police, acting on behalf of the National Crime Agency, arrested three men in connection with drugs offences in a raid at an address in Morley, Leeds, earlier today.
"West Yorkshire officers are working to make the site safe.”
The drama led to nearby Seven Hills Primary School being placed on lock down for a time, according to reports.
However, it remains unclear whether this was on the instruction of police or a decision taken by the school.
Nobody at the school in Appleby Way could be reached for comment.