Managua (AFP) - Armed riot police and pro-government paramilitaries on Monday attacked barricades manned by anti-government activists in the Nicaraguan capital, plunging neighborhoods into violence and chaos in an attempt to stamp out a two-month-old uprising against President Daniel Ortega.

The government offensive launched overnight into the early morning comes as Ortega enters his fifth day of silence regarding the Roman Catholic Church's proposal to restart talks aimed at calming the political crisis.

Cracks of gun fire resounded through the streets of Managua as television footage showed turbulent scenes of armed security forces on foot and in trucks chasing young men away from street barricades.

Activists attempted to push them back by throwing rocks and setting off homemade mortars.

The violence appeared to have cooled by mid-afternoon, a few hours after Silvio Jose Baez, an auxiliary bishop of Managua, had urged residents to stay inside their homes.

"It is very dangerous because of the presence of violent gangs," he wrote on Twitter. "Don't risk life in vain."

The protests that began April 18 over controversial pension reforms have exploded into a mass effort to pressure the president's exit.

At least 139 people have been killed in clashes with security forces and armed gangs loyal to Ortega, according to the Nicaraguan Center for Human Rights (CENIDH), which also said more than 1,000 had been injured.

Government security forces early Monday swept into seven neighborhoods, forcefully clearing barricades on the main Juan Pablo II avenue that connects the capital's north and south, activists said.

Hooded pro-Ortega armed civilians meanwhile broke down barricades that residents had built in adjacent streets to "protect" themselves from roving gangs.

- 'Severe democratic crisis' -

The blockades -- which are guarded by mostly young men wielding slingshots and mortars -- are found on nearly 70 percent of roads, crippling transportation and commerce in more than half of the country's departments.

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Similar attacks in the city of Sebaco, 90 kilometers north of Managua, left one dead on Sunday, according to the CENIDH.

Police meanwhile said that 15 hooded individuals attacked a police outpost in Mulukuku municipality in the Caribbean north of the country, killing two officers and one gang member. One police officer was also kidnapped.

In Leon, 90 kilometers northwest of Managua, civic groups called for work stoppages and school closings for 24 hours to protest the government's repressive actions.

Ortega, a leftist who has held the presidency since 2007, has remained silent since last Thursday's meeting with the Church, when he requested a "period of reflection" to mull over the bishops' mediation proposal.

The US Embassy in Nicaragua released a statement Monday voicing support for Church-led dialogue, saying Caleb McCarry, top staffer of the Senate Foreign Relations Committee had traveled to the country on Saturday to "discuss the severe democratic crisis."

He along with Ambassador Laura Dogu met the presidency and bishops as well as a civic alliance, the statement said.

"The United States respects Nicaragua's sovereignty and understands that the ultimate solution to the current conflict must come from Nicaraguans," the statement said, adding Washington aimed to "respectfully support" talks "in a way that is helpful and acceptable to all parties."

Also on Monday Nicaragua's Association of Freight Carriers (ATN) announced the suspension of all national and international shipments because of the blockades, which have stranded some 6,000 trucks.

"Dialogue is the only viable solution for Nicaragua to come out of the crisis," the association's president Marvin Altamirano told journalists.

- 'Language of repression' -

Nicaraguans have taken to the streets en masse to demand the ouster of Ortega, who first came to power in 1979 at the head of a communist junta installed by Sandinista rebels.

A major political force for the better part of four decades, he is now serving a third consecutive term as president due to end in 2022.

A key demand of activists is to bring forward the next presidential election and attempt to vote him out, but so far Ortega shows no signs of relinquishing his grip.

As part of the talks proposal bishops had presented the leftist leader with a plan to expedite the poll and institute electoral and constitutional reforms.

Repression has continued at equal if not greater intensity since that meeting, with four deaths reported in the municipalities Managua, Masaya, Sebaco and Jinotega resulting from pro-government attacks on activists.

During last week's meeting with Ortega, Bishop Baez said he voiced that "using only the language of repression in Nicaragua results in moving further from reality."

It "aggravates the political crisis and the pain of the people, and serves to destroy the national dialogue," he said.