BELGRADE, SERBIA -- Tens of thousands of people rallied in Serbia's capital on Friday for a third time in a month in protest at the government's handling of a crisis after two mass shootings in the Balkan country earlier this month, even as officials rejected the criticism and ignored their demands.

In a show of defiance, the nationalist right-wing party of autocratic Serbian President Aleksandar Vucic organized a counter-protest in a town north of Belgrade attended by thousands of his supporters.

The opposition protesters in Belgrade were chanting slogans against Vucic, demanding the resignations of two senior ministers and the revocation of broadcasting licences for two TV networks which, they say, promote violence and glorify crime figures.

Prime Minister Ana Brnabic and other government officials attended a parliamentary session on Friday focusing on the May 3 and 4 shootings and the opposition demands to replace the interior minister and the intelligence chief following the carnage that left 18 people dead, many of them children.

The two shootings stunned the nation, especially because the first one happened in an elementary school in central Belgrade when a 13-year-old boy took his father's gun and opened fire on his fellow students. Eight students and a school guard were killed and seven more people wounded. One more girl later died in hospital from head wounds.

A day later, a 20-year-old used an automatic weapon to randomly target people he ran into in two villages south of Belgrade, killing eight people and wounding 14.

Brnabic rejected allegations that the populist authorities were in any way responsible for the shootings. Instead, she accused the opposition of fuelling violence in society and threatening President Aleksandar Vucic. Brnabic blasted the opposition-led protests as "purely political", saying they were intended to topple Vucic and the government by force.

"You are the core of the spiral of violence in this society," Brnabic told opposition lawmakers. "You are spewing hatred."

She also said that "everything that has happened" in Serbia after the mass shootings was "directly the work of foreign intelligence services," adding that her government could be changed only by the will of the people in elections and not on the streets.

The opposition gathering Friday evening outside the Parliament building in Belgrade, is the third since the shootings. The two previous gatherings drew tens of thousands of people who marched peacefully, only occasionally chanting slogans against Vucic.

Authorities have launched a gun crackdown in the aftermath of the shootings and sent police to schools in an effort to boost a shaken sense of security.

Faced with public pressure, the increasingly autocratic Vucic has scheduled a rally of his own for next week in the capital while suggesting that the entire government could resign and a snap vote be called for September.

He also attended his party's rally Friday in the town of Pancevo that started at the same time as the opposition-led protest in the capital.

In his speech, Vucic mirrored his prime minister's narrative, suggesting the opposition protests had been orchestrated from abroad. He accused his political opponents of trying to take power through violence and "destroy Serbia."

"There can be no (coming to) power without elections," Vucic told the crowd. "I will never serve foreigners."

Earlier in the Parliament, Interior Minister Bratislav Gasic, whose resignation is demanded by protesters, defended the police measures in the aftermath of the shootings. He also told Parliament that citizens have so far handed over more than 23,000 weapons and over 1 million rounds of ammunition since a one-month amnesty was declared on May 8.

"Police could not have known or predicted that something like this would happen," he said of the school shooting, the first ever in Serbia.

Gasic also confirmed media reports that a man who was recently released from a mental hospital fired an anti-tank missile on Thursday at an empty house from a grenade launcher in the town of Ruma, outside Belgrade. No one was injured in the incident, and Gasic said two people were arrested.

Serbia is flooded with weapons left over from the wars of the 1990s, including rocket launchers and hand grenades. Other gun-control measures declared in the wake of the shootings include better control of gun owners and shooting ranges, a moratorium on new licences and harsh sentences for possession of illegal weapons.

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Dusan Stojanovic contributed.