Earlier, the police reported arrest of two men in connection with the incident.
"Detectives investigating last night's explosion outside Bishop Street courthouse in Derry/Londonderry have arrested a further two men. The men aged 34 and 42 were arrested in the city this evening", the police said.
One of the main versions of the investigation of the incident is the involvement of the Northern Irish terrorist group New IRA (Irish Republican Army). The investigation found that the blasted car — a pizza delivery van — had been hijacked shortly before the incident in the same city, and a small-capacity improvised explosive device had been put in it.
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The police also confirmed that no one had been injured in the explosion.
Over the past few years, the New IRA has carried out several terrorist attacks in the region. In particular, on 22 February 2017, its militants attempted to blow up a police car in Derry.
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In the 1970s and 1990s, clashes between local Catholics and Protestants occurred in Northern Ireland, accompanied by terrorist attacks. The attacks also occurred in the 2010s.