Ricardo Alarcon accuses the US of the 'privatisation of war'
Cuba has accused a US contractor it arrested last month of working for the US secret services.
The unnamed American was detained at Havana airport on 5 December. He was not seen by US consular officials until 28 December.
Cuban Parliament President Ricardo Alarcon said the man was still under investigation and had not been charged.
This incident suggests US-Cuba ties have once again taken a turn for the worse, the BBC's Michael Voss says.
Relations between the two countries had started to thaw after US President Barack Obama came to office in January last year.
Washington said the detained man was working for a US company called Development Alternatives, which is part of a US government programme aimed at promoting civil society and democracy in Cuba.
"This is a gentleman hired by a company that hires for the American secret services and is now the subject of an investigation," Mr Alarcon told reporters in Havana.
He described it as an example of the "privatisation of war" by the US, which hires people to be "agents, torturers, spies".
In an earlier speech, President Raul Castro alleged the man had been illegally supplying opposition groups with advanced communications equipment.
He also accused the US of continuing its attempts to subvert and destroy the revolution, our correspondent in Havana reports.