Colombia has withdrawn negotiators from Ecuador, bringing an abrupt end to year-long peace talks between the Colombian government and the National Liberation Army (ELN).

The move follows a series of attacks on government targets on Wednesday just hours after a ceasefire between the Colombian military and ELN expired.

The Colombian military accused the armed group of responsibility for four different attacks that wounded at least two marines and disrupted an important oil pipeline in the east of the country.

Colombian President Juan Manuel Santos condemned the "inexplicable" violence at a press conference on Wednesday and restated his commitment to the peace process.

"We were always, I repeat, always ready to extend the ceasefire with the ELN and negotiate very quickly a new cycle of talks.

"The ELN not only rejected this process but chose to restart their terrorist attacks on the very day that they were obliged to initiate the new round of negotiations," Santos said.

ELN representatives have been in neighbouring Ecuador for months holding talks with Colombian government officials.

In a statement on its website, ELN said the incidents took place within the "complex conflict situation" in Colombia.

"It should not alter the course of the [peace] conversations to reach a political way out of the conflict," it said.

Al Jazeera's Alessandro Rampietti, reporting from the Colombian capital Bogota, said the future of the peace process is now uncertain.

"Santos is insisting that this is not a formal suspension of the talks, but it definitely really looks like that," he said.

"Analysts were very pessimistic ... We can also expect the Colombian military to resume bombing attacks in different areas of the country, and a full-blown return of the hostilities at least for the time being."

Uneasy peace

The ELN began peace negotiations with the government in February 2017 after more than three years of failed attempts.

The rebels are Colombia's last violent group after a peace deal was struck in 2016 with the Revolutionary Armed Forces of Colombia (FARC).

ELN wanted to negotiate a similar agreement as FARC did, which allows rebels to form a political party and avoid jail time in exchange for confessions and laying down arms, however, it has been difficult to reach a consensus.

"The talks have been complicated by a lack of confidence between the parties since the beginning of this difficult process and a lack of real results apart from the ceasefire, which [although it] has seen a number of violations, was considered a success by practically everybody inside and outside the country. Everybody here was expecting an extension," said Rampietti.

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The ceasefire began in October and resulted in 102 days without any attacks on the country's infrastructure or security forces.