Prosecutors in El Salvador are investigating alleged secret negotiations between government officials and a prominent organized crime gang that has long terrorized the Central American nation.

The probe follows the publication of a newspaper investigation into alleged government links with the country's infamous Mara Salvatrucha gang.

Online newspaper El Faro reported that the government of President Nayib Bukele held talks last year with leaders of the feared gang -- otherwise known as MS-13 -- offering improved prison conditions in exchange for guarantees that the gang would reduce the country's notoriously high murder rate.

The reported talks would contradict a pledge by 39-year-old Bukele -- elected last year on a pledge to get tough on crime -- not to negotiate with the gang, which EL Salvador's courts have designated a terrorist group.

El Salvador is one of the world's most dangerous nations, with an average of 35.6 homicides per 100,000 people last year.

Attorney General Raul Melara announced late Monday that his office had opened an investigation into the explosive allegations.

"We are seeking information to determine if there are indeed negotiations between government officials and the gangs," he said.

"We are not going to allow deals with terrorists. We will not allow the institutionalization of benefits for gang members."

- Searches over 'several days' -

Prosecutors on Monday carried out searches of cells at the maximum security prisons of Izalco and Zacatecoluca, which houses gang members, in connection with the allegations.

They also raided state penitentiary offices in the capital San Salvador.

Searches will last "several days," said Melara.

Penitentiary chief Osiris Luna, who is also the deputy justice minister, said the institution was cooperating fully with prosecutors: "We have given them total access. They can gather all the information they require."

Bukele, in a tweet, insisted his administration had nothing to hide. "He who owes nothing, fears nothing," he wrote.

His government, elected in June 2019 on promises to curb violence, has deployed large numbers of police and soldiers in the most volatile areas of the country as part of a so-called Territorial Control Plan.

It includes isolating imprisoned gang leaders to cut off their communications with the outside world, and combating racketeering, one of the main sources of income for criminal gangs.

The justice ministry said the plan had already cut the country's homicide rate from 52 to 36 per 100,000 inhabitants. It forecasts lowering it further, to 21 per 100,000, by the end of this year.

El Salvador "has become a reference in the region in terms of security," Justice Minister Rogelio Rivas boasted recently on Twitter.

But according to El Faro, the underground negotiations were not only about lowering the homicide rate, but also aimed at securing MD-13's support for Bukele's Nueva Ideas (New Ideas) party ahead of polls due next year.

Bukele has dismissed the report as "ridiculous," and the government pushed back by inviting journalists, including AFP, to visit prisons to see conditions for themselves.

- 'Official documents' -

One of the report's authors, Oscar Martinez, told AFP his newspaper's investigation was based on "official documents."

"So far, no one in the government, no official, has said that the 108 pages of official documents that our investigation is based on, are false. They are official documents," said Martinez.

Jose Miguel Vivanco, executive director for the Americas at Human Rights Watch, said on Twitter that Bukele's promises "to improve security and fight corruption were a lie."

Accusations of government appeasement of the powerful criminal gangs, or maras, are nothing new in El Salvador.

Former president Mauricio Funes, now exiled in Nicaragua, and former defense minister General David Munguia are being prosecuted for negotiating a pact with the maras in 2012.