BELGRADE (Reuters) - Serbian police have seized a weapons cache including more than 100 hand grenades and 30 kg (65 lb) of explosives, Interior Minister Nebojsa Stefanovic said on Wednesday, the biggest haul uncovered in 15 years in a country awash with illegal arms.

Ten people were arrested in raids in the northern towns of Apatin and Sombor which also yielded 12 anti-armor grenades, two rocket launchers, detonators, eight assault rifles, a heavy machine gun, semi-automatic rifles and 6,000 bullets.

"We are worried not only because of the probable use of weapons in our country, but also because of the probability they could have ended up in European capitals and been used in criminal acts," he said.

Stefanovic said the investigation was continuing. "There are always concerns about the terrorist threat," he said.

Plentiful arms supplies, including automatic and anti-tank weapons, remained in private hands after the Yugoslav wars of the 1990s. Many are now in the caches of criminal groups who regularly smuggle weapons outside the region.

Some of the assault rifles used by Islamist militants who killed 130 people in Paris a year ago were produced in the 1980s in the former Yugoslavia's state arsenal.

The latest weapons find comes after several gangland slayings in Serbia and at a time of tension in the region.

Authorities in neighboring Montenegro are investigating an alleged plot to sway an election there last month, when 20 Serb citizens were arrested and accused of planning armed attacks.

Last month, the Serbian police moved Prime Minister Aleksandar Vucic and his family to a safe location after uncovering a weapons cache near his parents' home, which he regularly visits.

(Reporting by Aleksandar Vasovic; Editing by Mark Trevelyan)