Following Iran's launch of more than 300 drones and missiles toward Israel last Saturday, some experts raised the possibility that North Korean parts or military technology could have been used for Iran's missile salvo against Israel, citing close military cooperation between Pyongyang and Tehran, Yonhap news agency reported.

"We are keeping tabs on whether the North Korean technology was included in Iran's ballistic missiles launched against Israel, given North Korea and Iran's missile cooperation in the past," the National Intelligence Service (NIS) said.

Having established diplomatic ties in 1973, Pyongyang and Tehran are known to have close ties while under international sanctions for their weapons programs. The countries have been suspected of exchanging missile parts and technology, especially during the 1980-1988 Iran-Iraq war.

In 2006, the Chief Commander of Iran's Revolutionary Guards publicly acknowledged that his country had obtained Scud-B and Scud-C missiles from North Korea during the war, but no longer needed Pyongyang's assistance.

A 2019 report by the US Defence Intelligence Agency showed Iran's Shahab-3 ballistic missiles were developed based on North Korea's mid-range Rodong missiles. The Khorramshahr missile that Iran has developed is believed to be technically linked to North Korea's Musudan missiles.

Matthew Miller, a State Department spokesperson, said on Tuesday that the US is "incredibly concerned" about long-suspected military cooperation between North Korea and Iran.

In January, the NIS confirmed suspicions that North Korean-made weapons are being used by the Hamas militant group in its war with Israel despite Pyongyang's repeated denial of its arms transactions.