The head of Greece's intelligence service (EYP) has resigned, the prime minister's office said amid mounting pressure on the government to shed light on the use of surveillance malware, Reuters reported.

EYP head Panagiotis Kontoleon has resigned following erroneous practices discovered during legitimate wiretapping procedures, the Prime Minister's Office said in a statement.

Earlier this week, it was reported that Kontoleon admitted that his office was spying on Thanasis Koukakis, a financial journalist working for CNN in Greece.

The Prime Minister's Office said Prime Minister Kyriakos Mitsotakis' top aide, Secretary General Grigoris Dimitriadis, also resigned without giving any details. EYP reports to the Prime Minister's Office.

The government says Greek authorities do not use spyware allegedly used to hack into the journalist's phone or do business with companies that sell it.

In April, a Greek prosecutor launched an investigation into Koukakis' claim that his smartphone was infected with spyware.