Clashes have erupted between opposition protesters and members of Venezuela's armed forces, as opposition leader Juan Guaido called for more protests against President Nicholas Maduro.

National Guard troops on May 1 fired tear gas at protesters who attempted to block a highway close to an air base in eastern Caracas where Guaido had called for a military uprising against Maduro.

The clashes came one day after Guaido called for a military uprising to oust Maduro -- a call that appeared to fall short.

Some protesters said they were disappointed by the failure of the military to respond to the call to oust Maduro. Others said they were frustrated by the relatively small turnout of demonstrators.

Maduro has accused Guaido of trying to stage a coup.

Meanwhile, the U.S. national security adviser said that Maduro was surrounded by "scorpions in a bottle" and it was only a matter of time before he leaves power.

John Bolton told reporters at the White House that key figures in Maduro's leadership, including the defense minister and head of the presidential guard, had been "outed" as dealing with the opposition.

In an April 30 interview with CNN, U.S. Secretary of State Mike Pompeo claimed that Maduro was ready to leave his troubled country for exile in Cuba but was persuaded by Russia to remain.

That assertion was rejected by Russian Foreign Ministry spokeswoman Maria Zakharova, who said Pompeo's statement was part of an "information war."

Pompeo also spoke with his Russian counterpart, Sergei Lavrov, on May 1, and the Russian diplomat scolded Pompeo for what the Foreign Ministry called the United States' "aggressive steps."

"Washington's interference in the internal affairs of a sovereign state, and threats against its leadership are a gross violation of international law," the ministry said in a statement. "The continuation of these aggressive steps will be met with the most severe consequences."

The State Department said in a statement that during the call with Lavrov, Pompeo "stressed that the intervention by Russia and Cuba is destabilizing for Venezuela and for the U.S.-Russia bilateral relationship."

Pompeo "urged Russia to cease support for Nicolas Maduro and join other nations, including the overwhelming majority of countries in the Western Hemisphere, who seek a better future for the Venezuelan people," department spokeswoman Morgan Ortagus said in a statement.

Russia, Iran, China, and Cuba are among countries supporting Maduro, who started a second term in January following a May 2018 election marred by an opposition boycott and claims of vote-rigging, leading to mass street protests.

Russia, which has substantial economic ties to Maduro's government, in March sent planes carrying nearly 100 military personnel the U.S. government believes included special forces and cybersecurity experts to Venezuela.

Also May 1, a top Pentagon official told U.S. lawmakers that the Defense Department had not been given orders to prepare for war and was stressing support for diplomacy.

Asked whether the U.S. military had been given instructions to prepare for conflict, acting Assistant Secretary of Defense for International Security Affairs Kathryn Wheelbarger told the House Armed Services Committee, "We of course always review available options and plan for contingencies."

"But in this case we have not been given [the] sort of orders that you're discussing, no," Wheelbarger said.

In a separate congressional hearing, the chairman of the U.S. Joint Chiefs of Staff said that the U.S. military was also focused on collecting intelligence on the situation in Venezuela.

"We are doing what we can now to collect intelligence and make sure we have good visibility on what is happening down in Venezuela and also be prepared to support the president should he require more from the U.S. military," General Joseph Dunford said.

With reporting by AP, AFP, Reuters, dpa, and TASS