Quito, Ecuador - Letter bombs were sent to at least five journalists working in TV and radio stations in violence-plagued Ecuador Monday, one of which exploded without causing serious injury, Interior Minister Juan Zapata said.

The prosecutor's office said it had opened an investigation into the crime of terrorism, without stating why the news stations were specifically targeted, or by whom.

The interior minister said the envelopes were sent from the town of Quimsaloma, in the coastal province of Los Rios. Three were sent to Guayaquil in the southwest and two to the capital Quito.

The 'device is indeed the same in all five places,' Zapata told reporters.

In the port city of Guayaquil, journalist Lenin Artieda of the Ecuavisa private TV station received an envelope containing a pen drive which exploded when he inserted it into a computer, his employer said.

Artieda sustained slight injuries to one hand and his face, said police official Xavier Chango. No one else was hurt.

Chango said the USB drive sent to Artieda could have been loaded with RDX, a military-type explosive.

Another package addressed to journalist Carlos Vera was intercepted by the police at a courier company in Guayaquil and did not reach its destination, Zapata said.

Elsewhere in Guayaquil in Ecuador's southwest, the prosecutor's office said a letter bomb was also sent to the offices of TC Television.

There is 'an absolutely clear message to silence journalists,' said the minister.

'New escalation'

The Teleamazonas chain later said it had also received a USB stick at its offices in Quito 'with the same characteristics' as the one sent to Ecuavisa.

The Fundamedios NGO which advocates for press freedom, said the three 'attacks used the same modus operandi.'

Envelopes with USB sticks were addressed to Artieda as well as to Mauricio Ayora of TC Television and Milton Perez of Teleamazonas, it said in a statement.

The envelope addressed to Artieda contained a threat against the journalist, said Fundamedios.

The one to Teleamazonas, it added, contained a note that claimed the stick contained information on 'Correismo' -- a political movement named after former president Rafael Correa.

The letters represented 'a new escalation in violence against the press, said Fundamedios, and called for 'immediate intervention of the State.'

The government said in a statement that it 'categorically rejects any form of violence perpetrated against journalists and media outlets.'

Any attempt to 'intimidate journalism and freedom of expression are repugnant,' it added.

The CDH human rights watchdog also condemned the attacks on media 'in the context of growing insecurity in Ecuador.'

Ecuador is sandwiched between Colombia and Peru, the world's two largest cocaine producers, and has itself become a hub for the global drug trade in recent years.

Guayaquil is one of its most violent cities, with frequent clashes among criminal gangs disputing drug trafficking routes.

President Guillermo Lasso has declared war on gangs who control the drug trade from prisons engulfed by extreme violence and riots that have left more than 400 inmates dead since 2021.

Ecuador has seen its murder rate jump from 14 per 100,000 inhabitants in 2021 to 25 per 100,000 in 2022.

Last year, the RTS TV station came under gunfire, and in 2020 a bomb exploded at Teleamazonas.