The firm, based in the southern port city of Malaga, exported "engines and spare parts for tanks and armoured personnel carriers" worth 2.8 million euros (around $ three million), the Guardia Civil police said a statement.

The exports were falsely labelled as parts for civilian trucks, and the company did not have an export licence.

The owner and another suspect, who was not arrested, are being investigated on suspicion of smuggling defence material, police said.

The company also provided technical assistance for "the modernisation of many armoured vehicles" belonging to the Saudi armed forces, it said.

In Spain, companies wanting to export weapons or military equipment must be listed on a special register and have a licence approved by the authorities for each shipment.

"Some of the material" exported was "used in armoured vehicles used in the Yemen conflict," it said.

Since 2014, Yemen has been embroiled in a bloody civil war pitting the Iran-backed Huthi rebels against the country's internationally recognised government, which since 2015 has been supported by a Saudi-led coalition.

Hundreds of thousands of people have been killed in the conflict, which has sparked one of the world's worst humanitarian crises.

Saudi Arabia is one of the world's leading arms importers, according to the Stockholm International Peace Research Institute (SIPRI).

Arms sales to Saudi are regularly criticised by NGOs like Amnesty International which say some of the weapons delivered to Riyadh are ultimately used in Yemen.

Following the 2018 murder of journalist Jamal Khashoggi, which US intelligence linked to Saudi Crown Prince Mohammed bin Salman, Germany announced an embargo on arms sales to Riyadh, which it lifted in January.