The police have concluded that no hazardous materials were found in thousands of suspicious international parcels reported nationwide.

The National Police Agency said Friday that the packages were concluded to contain no harmful substances to human health after unknown sample tests were conducted by the Korea Institute for Defense Analyses.

Earlier the institute carried out tests on radiation and biochemicals and confirmed the parcels were free of dangerous materials but conducted an additional sample test after officials at a welfare facility in Ulsan, who initially reported the suspicious arrivals, complained of symptoms such as numbness in the arm. 

Following the conclusion, the police have also decided to end their investigation into potential terrorism implications. Officers believe the parcels were sent in what's known as a "brushing scam" where unordered items are sent to random people to manipulate product reviews. Police are looking into whether charges of illicit personal information collection can be brought against the senders.

As most of the parcels came from China via Taiwan, police have also requested cooperation from the Chinese police.

As of 5 a.m. Thursday, over 36-hundred such deliveries were reported nationwide.