By Aleksandar Vasovic

BELGRADE (Reuters) - Serbia's Prime Minister Aleksandar Vucic said on Sunday he did not believe he had been subject to an assassination attempt, seeking to calm tensions after the discovery of a cache of heavy weapons on a route regularly taken by his motorcade.

The weapons, which included a rocket launcher, hand grenades and rifle ammunition, were found in bushes in the neighborhood of Jajinci, near a crossroads where Vucic's motorcade normally slows on his frequent visits to his parents' home.

"Someone could have simply dumped weapons there by chance," he told reporters at a press briefing held to discuss a visit by an International Monetary Fund mission. "This was not an assassination attempt," he said. "Nobody touched me."

Vucic said a tipoff led to the discovery of the weapons and that he was immediately taken to an undisclosed safe place. No arrests have been made in connection with the find.

He appeared to have no extra security at Sunday's news conference, which had been scheduled long in advance and was held in the usual central government building.

Nevertheless, police were out in greater force than normal in Belgrade, patrolling in streets around government buildings. Security around top officials in Serbia has been tight ever since the assassination 13 years ago of Zoran Djindjic by Serb nationalists with links to the mafia and secret police.

The weapons find is the latest in a series of recent events that has put the Balkans on edge and sparked rumors and conspiracy theories. Five days ago, Montenegro thwarted a suspected plot by a group of Serbian citizens to sway the outcome of its Oct. 16 election. There have also been several recent mafia-style assassinations among criminal groups in Belgrade.

Although the region has been peaceful since the end of a series of wars in the 1990s sparked by the collapse of federal Yugoslavia, the people of the Balkans are still deeply divided along ethnic and religious lines.

Its countries including Serbia are awash with hundreds of thousands of illegal weapons left over from the wars, adding to fears of a flare-up of previous conflicts. Many such arms are in the hands of criminal groups.

Vucic said he was awaiting a forensic report from the site.

(Reporting by Aleksandar Vasovic; Editing by Thomas Escritt and Raissa Kasolowsky)