BOGOTA (Reuters) - The United States has no timeline for a change in government in Venezuela, a U.S. top official said, but is certain embattled President Nicolas Maduro will not remain in power.

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Washington has imposed a raft of sanctions against Maduro’s government in an attempt to pressure him out of power and allow opposition leader Juan Guaido to take control.

“There’s no timeline on a return to democracy but it is coming, of that I’m certain,” James Story, the U.S. charge d’affaires for Venezuela, said in an interview. “This was never going to be something that was quite easy.”

Maduro blames U.S. sanctions for the country’s economic problems and dismisses Guaido as a U.S. puppet. More than 3 million Venezuelans have fled hyperinflation, food and medicine shortages and political crisis.

Guaido in January invoked the country’s constitution to assume an interim presidency, arguing Maduro’s 2018 re-election was illegitimate, and while most Western nations have recognized Guaido as head of state, Russia, China and Cuba have stood by Maduro.

Maduro broke off diplomatic relations with the United States after it recognized Guaido. The U.S. State Department said last month it would withdraw all diplomatic personnel from the OPEC nation, arguing they had become a “constraint on U.S. policy.”

Arguments that U.S. sanctions caused Venezuela’s problems “don’t hold water” said Story, who visited Colombia to accompany U.S. Secretary of State Mike Pompeo on a Sunday trip to the border city of Cucuta.

“The sanctions that have hit the big parts of the economy are very recent,” he said. “We have multiple options when it comes to how we engage on economic sanctions, how we deploy them, how we use general licenses, how we make sure that we’re trying to have a minimum impact on people.”

Corrupt officials are to blame for shortages, he added.

“These were people who weren’t focused on doing the right thing for their citizens but rather people who were focused on self-enrichment.”

“We’re trying to bring in foodstuffs and other types of medicine in order to support the Venezuelan people who are suffering. And the Cubans import intelligence officers who are only focused on repressing dissent and making certain that the military doesn’t oust Maduro,” said Story.

But humanitarian aid, largely rejected by Maduro, may be able to enter Venezuela because of individuals, Story said.

“I think you’ll see more aid come in because you’ll see more desperate people attempting to help their fellow Venezuelans.”