KIEV, June 11 – Gunpowder carried by a tram passenger in Dnipropetrovsk suddenly ignited on Monday, injuring nine people and initially causing a terror scare as Ukraine co-hosts the Euro-2012 soccer tournament.

The ignition was later ruled by the authorities to be an “accident” after teams of security service agents and police had inspected the site. Dnipropetrovsk is not one of four Ukrainian cities that are actually hosting European soccer matches.

“The gunpowder ignited for some unknown reason. Either it was very hot or the man dropped it on the floor,” Volodymyr Polishchuk, a spokesman for the Interior Ministry, said.

Registered hunters in Ukraine routinely buy gunpowder to assemble their own rounds.

The development initially triggered a major terror scare in the city as it comes six weeks after four separate bombs had detonated in a series of coordinated blasts in Dnipropetrovsk. The bombs were then planted in trash bins next to tram stops.

Up to 31 people were injured at the end of April when the devices exploded at short intervals.

Dnipropetrovsk, an important industrial and technological hub and the birthplace of many of Ukraine's political elite, is located about 150 miles away from Donetsk and 250 miles southeast of the capital Kiev. Kiev, Donetsk, Lviv and Kharkiv are hosting the Euro games.

Dnipropetrovsk is one of Ukraine's biggest industrial hubs and was a key center of the nuclear, arms and space industries in Soviet times.

The bombings have also added to political tension in Ukraine, already high following last year's conviction of President Viktor Yanukovych's opponent, former Prime Minister Yulia Tymoshenko, on abuse-of-office charges and a fresh tax evasion trial against her.

Tymoshenko was born in Dnipropetrovsk.

The government and the opposition have traded accusations of seeking to exploit the blasts for political purposes.

A month after the blasts, the authorities arrested two men in connection with the April explosions, according to Interior Minister Vitaly Zakharchenko.

The two suspects are from Dnipropetrovsk and they had tried to demand $4.5 million from the authorities not to go ahead with their allegedly further planned explosions.

State media said the men are under 40 and have never served in the military, which could mean they are foreign.

The opposition, meanwhile, suggested it could be part of a government plot to divert attention from the ongoing imprisonment of Tymoshenko.

Tymoshenko was jailed for seven years in October for abuse of power during her time as prime minister. Opposition groups have said the trial was politically motivated. (nr/ez)