Sen. Marco Rubio, R-Fla., said Wednesday that he would oppose any candidate to be the next ambassador to Cuba until the Castro regime stops imprisoning and oppressing democracy activists on the island, activity he says has stepped up since Obama's December announcement that he wants to normalize relations.

Rubio declared his intentions just minutes before President Obama was expected to announce the establishment of embassies in Havana and Washington.

"It is time for our unilateral concessions to this odious regime to end," he said in a statement released Wednesday morning.

Obama and Secretary of State John Kerry will announce the opening of embassies Wednesday morning, a major step in normalizing relations between the two countries. The announcement is being made a few weeks after the administration dropped Cuba from its list of terrorist-sponsoring nations — Cuba had insisted on that change before allowing embassies to open.

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