No one thought to mention it when they heard whispers and rustling in the bushes near the police station in Capitan Gimenez, assuming it was the hushed voices of lovers in the dark.

The two officers on guard had just finished dinner when gunmen ambushed the station, killing them both. Another had gone out to buy credit for his mobile phone. In this remote corner of northern Paraguay, cattle-rustling is the most common crime.

You can't forget something like that, said Jose Gamarra, 24, another officer at Capitan Gimenez who was also out when the group of as many as 10 heavily armed attackers struck the village station one night in late September.

Officials were quick to blame the Paraguayan People's Army, or EPP by its Spanish initials, a small left-wing group that mixes violence with a revolutionary rhetoric reminiscent of the guerrilla movements that sprang up across Latin America in the 1960s and 1970s.

Most such ideological groups have faded away since then and criminal gangs linked to drug-trafficking are responsible for surging rates of violent crime in much of the region.

The EPP has gained prominence in recent years due to several high-profile kidnappings and daring raids and President Fernando Lugo is under mounting pressure to close the net on the gunmen.

He has sent troops and more than 1,000 extra police to the group's heartland in the ranching provinces of Concepcion and San Pedro for a 60-day crackdown due to end next month. But catching the EPP's leaders will not be easy.

The group's armed members are thought to number no more than 20, relying on close friends and relatives for logistical support in a deprived and long-forgotten region where suspicion of the police runs deep.

Sending tanks isn't the answer. It's sending tractors, doctors and making sure people have shoes ... and roads, that would be a lot more effective, said Raquel Talavera, a lawyer who used to defend jailed members of the group.

Some opposition members of Paraguay's fractious parliament have threatened to start impeachment proceedings against Lugo if the security crackdown fails to yield results, said centre-right lawmaker Sebastian Acha.

There's going to be a lot of political pressure when the (operation) ends, which most opposition members from the traditional parties are going to use as a bargaining chip to force concessions from the president -- a job, a nomination, he said.

It is another potential headache for Lugo, whose presidency has been complicated by divisions in his ruling coalition, a lengthy cancer treatment and paternity claims by three women. He has admitted fathering one child when he was a bishop.

Almost every police station in Paraguay has a Wanted poster carrying mug-shots of the armed groups' leaders, offering rewards of up to one billion guaranis (about $250,000) for information leading to their capture.

It is a fortune in a region where few earn as much as the minimum monthly wage of about $400, but fear of reprisals and mistrust of authorities mean people are wary of speaking up.

If you talk, they'll harm you or your family so no one talks, said Vicenta Sanchez, 55, standing behind a stall selling fresh herbs in front of the church in Horqueta.

Everyone is scared of them, we're all afraid, she said.

An added discomfort for the president stems from several of the EPP leaders' past links to the Roman Catholic Church in Concepcion and San Pedro, where Lugo served as a bishop.

Their training was here in the church, but then they lost their way, said Nelson Ramirez, a priest in Horqueta as he sipped traditional yerba tea from a metal straw in the church hall.

They wanted to follow the Marxist path and because of that they were expelled from the seminary, he said. It's very painful for us.

Around the corner from the church, the police station is still scarred after a small, home-made bomb was thrown at the building in a suspected EPP attack in January. The nearby prosecutor's office was hit in a similar attack in September.

Officials deny Lugo has any links with EPP, whose activities are normally traced back to the late 1990s and the now defunct left-wing political party, Patria Libre.

The president was bishop of San Pedro for many years. That doesn't mean to say he has any connection to people who may have passed through, said Interior Minister Carlos Filizzola, calling the EPP criminals and playing down their political intentions.

COURTESY OF THE EPP

When the EPP kidnapped wealthy cattle rancher Fidel Zavala two years ago, they forced his brother to distribute free beef to low-income neighbourhoods, telling recipients the meat was courtesy of the EPP.

The group professes a Marxist ideology reminiscent of Cold War days, vowing to champion the rights of the landless poor who have suffered from the spread of huge cattle ranches and ever-expanding soybean farms in Paraguay.

In an email sent to local media last month and presumed genuine, the group referred to a titanic struggle of the EPP to help ... the poor and forgotten.

Zavala, the wealthy rancher, was freed after three months in captivity and the payment of a ransom estimated by a prosector at about $550,000.

A year earlier another rancher, Luis Lindstrom, was released for a ransom of about $300,000, according to prosecutor Guillermo Ortega, suggesting the EPP still has enough money to buy arms and pay people off.

Zavala told prosecutors the group's leaders are well-armed with M16 rifles, pistols and grenades.

Weapons have been stolen during raids on police posts, but officials say the EPP may buy from arms traffickers who operate in Paraguay's porous border areas, a transit route for Andean cocaine that is also home to marijuana plantations.

Authorities have long suspected the group of having links with Colombia's FARC leftist rebels, Latin America's biggest and most active insurgent group, though ties may have waned.

In the past they had a certain relationship with the FARC, but we don't know if this continues, Filizzola said.

Like the FARC, the EPP shelters in remote terrain. They set up camps and move 12 or 13 kilometres (8 miles) by foot every night, said deputy national police commander Aldo Pastore.

He warned of a possible upswing in violence when the security swoop ends, something Lugo will want to avert.

Continued operations have the potential to exacerbate political tensions in Paraguay that could put increasing strain on the government, said Grant Hurst, an analyst at IHS Jane's in London.

Two months since the attack in Capitan Gimenez, the officers say they are ready if the EPP come back.

We were prepared with the basics, as much as we could be ... Now we've got everything we need, Gamarra said as chickens scratched around in the shady back yard. (But) they've got one advantage; it's easy for them to find us.

(Additional reporting by Ximena Abente; Writing by Helen Popper; Editing by Kieran Murray)