Germany is investigating a suspected arson attack outside a defence firm in Munich, days after two sabotage attempts on the country's power grid.

Police arrested two people suspected of throwing incendiary devices and causing a fire at a construction site at the headquarters of Rohde & Schwarz.

Radar systems that detect, track and jam drones are among the products sold by the company.

The suspects, a 28-year-old woman and a 38-year-old man, who are both from Bulgaria, were arrested at a nearby petrol station, according to police from the German state of Bavaria.

The fire ‌caused no significant damage, and no one was injured, according to officials.

Rohde & Schwarz confirmed a police and fire brigade operation near its premises.

Bulgarian Interior Minister Ivan Demerdzhiev promised cooperation but declined to give details.

The suspected arson comes after sabotage attempts against the country's power grid and a month after an airport drone attack that Berlin and its allies blamed on Russia.

Allies rallied round after Germany blamed a drone attack in August at Leipzig/Halle airport on Moscow as part of hybrid warfare meant to intimidate and divide countries that have supported Ukraine since Russia's full-scale invasion.

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While investigations continue into the attempted sabotage of the country's power grid, the European Union is weighing up whether to implement more sanctions.

Russia has strongly denied involvement and on Thursday said it would close Germany's Goethe-Institut cultural centres, reciprocating similar moves from Berlin.

Poland and Britain have summoned Russian diplomats, as have other European allies.