Venezuela’s opposition is bracing for a severe political crackdown after Nicolás Maduro lashed out at the “diabolical pro-imperialist puppets” he claimed were trying to remove him from the presidency and vowed to imprison them all.

The struggle between Maduro and his challenger, Juan Guaidó, escalated dramatically last week with the detention of Guaidó’s right-hand man, Roberto Marrero.

Marrero, a 49-year-old lawyer, was accused of helping to run an anti-Maduro “terror cell” that was plotting a series of political assassinations and attacks designed to force Hugo Chávez’s successor from power.

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Maduro’s information minister, Jorge Rodríguez, on Saturday claimed the head of that supposed network was Guaidó’s political mentor, Leopoldo López. He accused the group of recruiting Central American mercenaries to carry out attacks on the political and military leaders of Maduro’s “Bolivarian revolution”.

Addressing a rally in Caracas on Saturday, Maduro hinted that Guaidó and other key opposition figures were also in his sights.

“In the coming days, we will certainly see more terrorists captured – whatever their names might be,” Maduro said. “There will be justice in Venezuela. We will not shy away from sending these crooks to jail – one by one – sooner rather than later … We have their names. We know their faces.”

On Sunday, the front page of one pro-Maduro tabloid, Últimas Noticias, fuelled opposition fears that Guaidó could face arrest. “Guaidó brought in assassins to commit acts of terror,” it said.

Any move against Guaidó could provoke a strong reaction from Washington. Donald Trump has thrown his weight behind efforts to unseat Maduro and the White House has warned of “significant” pushback if Guaidó is arrested or harmed.

Separately, two Russian air force planes landed in Venezuela’s main airport on Saturday carrying a Russian defence official and nearly 100 troops, according to a local journalist.

Phil Gunson, a Caracas-based analyst for Crisis Group, said he expected Maduro’s emboldened administration “to move in hard” on members of the opposition in the coming days.

“I think we will see more arrests … It seems like the hardcore around Maduro has decided to hang on at all costs … Everything we have seen in the last few days confirms the view that they are not considering a negotiated way out to this,” Gunson said.

At Saturday’s rally, which came exactly two months after Guaidó declared himself Venezuela’s rightful leader, Maduro claimed the “buffoonish” challenge to his rule was collapsing.

“The Bolivarian revolution will continue to lead the government and the people will continue to lead the motherland. There will be no empire, no puppets, no clowns and no parasites who can go against the will of the people of Venezuela,” said Maduro, who retains the support of China, Russia and Turkey.

In an interview with Reuters, Guaidó, who is recognised by most western governments but wields little concrete power within Venezuela, claimed it was Maduro’s regime that was crumbling. “They are isolated, alone,” he said. “They are falling apart day by day.”

Speaking to the Guardian last month, Guaidó conceded he could be jailed or forced into exile. “Doing politics in Venezuela is a risk and you can pay with your life … Obviously, there is a latent risk.”

Gunson said the fact that the threat of US military intervention appeared to have receded meant Maduro’s government now felt it had regained the initiative. “And if its default position before was to wait for this opposition phenomenon to deflate, they are now willing to take more direct action and to challenge the international community to do its worst.”

Gunson said Maduro’s inner circle would now be weighing the pros and cons of imprisoning Guaidó himself. “To lose him would be a really severe blow [to the opposition] – and both the government and the opposition know that. On the other hand, if Guaidó is put in jail then really the US and its key allies in the hemisphere would be obliged to do something severe.”