Kool and the Gang performed to rapturous applause in Havana
Cuban President Raul Castro has lashed out at the US, accusing Barack Obama's administration of endorsing efforts to undermine the communist regime.
In his annual address, Mr Castro said the US had sent a government contractor to supply dissidents. The unnamed US citizen was detained two weeks ago.
Speaking during his annual address, he said "the enemy is as active as ever".
The comments came as US band Kool and the Gang performed in Havana, in what some saw a sign of improving ties.
The concert, performed to an audience of thousands on Sunday, forms part of a series of recent cultural exchanges between Cuba and the US.
Mr Castro's comments were the first to acknowledge the detention of the US citizen, who works for a Maryland-based development organisation which regularly carries out work for the US government's agency for international development.
The contractor is reported to have been detained while distributing mobile phones and laptops. The US has made repeated requests for access to him.
"In the last few weeks we have witnessed the stepping up of the new administration's efforts in this area," Raul Castro told parliament.
"They are giving new breath to open and undercover subversion against Cuba."
He said the US citizen was working illegally in the country, distributing "sophisticated methods of communication to members of the civil society which they hope to form against our people".
Raul Castro said the US had allocated some $55m (38m euros; £34m) "to support a supposed democracy, the defence of human rights and aggression by radio and television against Cuba", apparently referring to the Marti network, which broadcasts to Cuba from US-run territory.
US President Barack Obama has made efforts to warm relations between the two states - easing the 47-year-old US trade embargo against Cuba, loosening travel restrictions for Americans wanting to visit Cuba and indicating he would be open to dialogue with Cuba's leaders.
In September, a senior US diplomat held high-level talks with the Cuban government during a visit to Havana, in the highest-level contact between the two sides in years.
But Mr Obama has said that, like previous American presidents, he will only consider a full lifting of the embargo once Cuba's communist government makes significant moves such as the holding of democratic elections.