He said he had recalled the leader of his team involved in peace negotiations with the rebels.

Mr. Santos won a Nobel Peace Prize in 2016 for his role in the deal with the FARC. But security analysts say that the ELN is far less organized and more ideological, and that Mr. Santos, whose term ends this year, has few viable paths to sign a peace agreement with a group that seems interested in continuing attacks.

“The ELN is disconnected from the electoral reality,” said Jairo Libreros, a professor at the Externado University in Colombia who follows the group. “They think that through acts of violence, society will rise up to call that the government signs a peace deal.”

The attacks appeared to be typical for guerrillas: a midnight raid on a military base in the eastern department of Arauca, in which commandos threw a grenade at soldiers guarding a post, injuring several them. Near the town of Aguazul, about 100 miles from Bogotá, the capital, another group bombed an oil pipeline, the government said.

The guerrillas defended their decision to resume attacks. The main purpose of the cease-fire, “to improve the humanitarian situation of the population, was hardly achieved by the regime,” they said in a statement. “We delivered on the objectives.”

The guerrillas said the attacks on Wednesday had “occurred in the middle of a complex situation of conflict in the country.” It called on the government to resume talks but did not offer another cease-fire.