Two US Republican lawmakers want to know if popular US pop star Beyonce and her husband, rap singer Jay-Z, had the US government's permission to travel to Cuba despite an economic embargo.

Representatives Ileana Ros-Lehtinen and Mario Diaz-Balart of Florida on Friday sent a letter to Adam Szubin, director of the Office of Foreign Assets Control at the US Treasury Department, requesting information on the type of license Beyonce and Jay-Z received before traveling to Cuba.

US singer Beyonce and her husband, rapper Jay-Z, tour Old Havana, Cuba, on Thursday. R&B's power couple was in Havana on their fifth wedding anniversary. Ramon Espinosa / Associated Press

"As you know, US law expressly prohibits the licensing of financial transactions for 'tourist activities' in Cuba," the pair wrote.

The lawmakers went on to say that these restrictions were in place because the Cuban government was listed by the US State Department as one of four state sponsors of terrorism.

"Cuba's tourism industry is wholly state-controlled; therefore, US dollars spent on Cuban tourism directly fund the machinery of oppression that brutally represses the Cuban people," Ros-Lehtinen and Diaz-Balart wrote.

Beyonce and Jay-Z created a stir on Thursday as they toured the streets of Old Havana, with hundreds of Cubans turning out to catch a glimpse of the US pop power couple.

Surprising visit

Celebrating their fifth wedding anniversary, they visited historical landmarks in the heart of Old Havana, which is a UNESCO World Heritage site. They snapped pictures and spoke with local residents.

Beyonce - who sang the US national anthem at US President Barack Obama's inauguration in January and performed in the Super Bowl half-time show in February - was wearing a short mustard yellow dress with black and white accents.

They ate at some of the city's best restaurants, danced to Cuban music, walked through historic Old Havana and posed for pictures with admiring Cubans, who recognized them despite the past half-century of ideological conflict that separates the United States and Cuba.

On Wednesday night they had dinner at La Guarida, one of Havana's most exclusive restaurants.

US citizens are not allowed to visit Cuba and spend money there unless they have special US government permission.