The top US diplomat for Latin America, Roberta Jacobson, met her Cuban counterpart Josefina Vidal behind closed doors for a third round of talks on normalizing relations, but the atmosphere of reconciliation was marred by protests over Washington's treatment of Venezuela.
As Jacobson touched down in the Cuban capital late Sunday, thousands of people attended a concert and rally to "support the Bolivarian (Venezuelan) people and government" in their mounting row with the United States.
His government arrested several people in the aftermath of the allegation, including the opposition mayor of Caracas.
US President Barack Obama responded by imposing new sanctions on seven senior Venezuelan officials, accusing them of cracking down on the opposition.
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He called Venezuela an "extraordinary threat to the national security" of the United States -- language Maduro said showed the US was itself an "imperialist threat."
The socialist leader then ordered "defensive military exercises" and asked Venezuela's National Assembly to grant him the power to rule by decree on defense and public safety matters -- a request voted through by his legislative majority Sunday.
Cuba's communist government called Obama's new sanctions "arbitrary and aggressive."
The concert on the steps of the University of Havana was a show of solidarity with the Venezuelan people's "suffering under the recent aggressive (US) escalation," an organizer told state-run newspaper Juventud Rebelde.
Unlike the previous two rounds of talks held since the historic US-Cuban rapprochement was announced on December 17, no press conference was scheduled for this week's meetings between Jacobson and Vidal, Cuba's top diplomat on US affairs.
Both sides are trying to iron out remaining issues with an eye on the upcoming Summit of the Americas in Panama on April 10-11.