(CNN) US Secretary of State Mike Pompeo spoke with Russian Foreign Minister Sergey Lavrov on Monday and called on Russia "to cease its unconstructive behavior" in Venezuela, State Department spokesman Robert Palladino said in a statement.

The United States "will not stand idly by as Russia exacerbates tensions in Venezuela," the statement said.

"The continued insertion of Russian military personnel to support the illegitimate regime of Nicolas Maduro in Venezuela risks prolonging the suffering of the Venezuelan people who overwhelmingly support interim President Juan Guaido," the statement said.

Russian planes arrived on Saturday at Simon Bolivar International Airport near Caracas, a diplomatic source in Caracas told Russian state-owned media RIA Novosti.

According to the source, the military came to consult with representatives of Venezuela on military-technical cooperation.

The source noted that "there is nothing mysterious" because the arrival of the planes is directly related to the implementation of contracts that were signed by the parties many years ago, RIA Novosti reported.

"Russia and Venezuela have a number of contracts that are under implementation, including contracts in the area of military-technical cooperation," he added.

Opposition leader accused of plotting 'terrorist acts'

In Venezuela, Jorge Rodriguez, the nation's minister of communication, spoke on national television Saturday to accuse opposition leaders, including National Assembly President Juan Guaido, of plotting "terrorist acts" in the country.

Rodriguez said some of the evidence was collected from the personal phone of Roberto Marrero, Guaido's chief of staff, who was detained in Caracas on Thursday and later accused of being involved in an alleged "terrorist cell" planning attacks against high-level political figures.

According to Rodriguez, Marrero coordinated the arrival of "hitmen" from El Salvador, Guatemala and Honduras to "kill members of the Venezuelan governments." He said that about 60 "hitmen groups" were prepared and "trained in Colombia," but that given the closure of the Colombian-Venezuelan border, only "30 groups entered Venezuela."

Marrero's lawyers have denied the claims and accused Maduro's regime of planting evidence.

CNN cannot confirm this information independently and Rodriguez did not present any evidence to support his claim.

This is not the first time the Venezuelan government has presented strong accusations against the Venezuelan opposition based on text messages, emails or pictures. And, with frequency, the elements are not presented by the Attorney General's Office, but by Rodriguez himself.

Guaido says evidence was planted

Guaido, recognized as interim president of Venezuela by more than 50 countries, on Saturday took to the streets of Barcelona, a city in northern Venezuela, with a clear message for Maduro: "You will not intimidate me, you will not intimidate us."

"You never planted our fields, but now you plant evidence a lot," Guaido said Saturday. "[Maduro's regime] fabricates evidence to persecute leaders, the people," he added.

Surrounded by hundreds of people waving flags and flashing cameras, Guaido asked his followers to stay on the streets demanding freedom and to not be afraid. "We have the support of important countries ... we are not alone," he said.

Guaido closed the rally by singing the national anthem and once again spoke directly to Maduro: "You believe you are going to intimidate us. Well, here we are, moving forward, holding our heads high, taking it all for the freedom of Venezuela," he said.

International banking meeting canceled

The Inter-American Development Bank, the largest source of development financing for Latin America and the Caribbean, called off its annual meeting in China next week after Beijing refused to grant an official visa to Ricardo Hausmann, Venezuela's representative designated by opposition leader Guaido.

China is one of the nations that does not recognize Guaido as Venezuela's leader.

The statement did not specify any reasons for the cancellation, but US Vice President Mike Pence suggested it was related to Guaido's pick. Writing for the Miami Herald on Friday, Pence said, "The Chinese are undermining the hemisphere's progress towards democracy by refusing to grant an official visa to Ricardo Hausmann, the lawful representative of Venezuela -- the first time in the bank's history that a host nation has refused to seat a member."

In a statement cited by Reuters, Geng Shuang, China's foreign minister, said Saturday that his country "had difficulties allowing" Guaido's representative and "regretted" the Inter-American Development Bank's decision to cancel the international gathering.

The meeting was to be held in Chengdu from March 28 to 31. The IDB issued a statement saying recommendations for the location and date of the 2019 annual meeting will be issued within 30 days.