MADRID — Imported coronavirus cases from the Americas are behind a series of new clusters in Spain.

Authorities on the Mediterranean island of Menorca said a young couple from the United States tested positive for the new virus and have self-isolated since their arrival last week.

Spanish authorities also believe that travelers from Bolivia are behind another cluster of infection in Spain’s southern Murcia region, where at least 19 cases have been reported.

The latest cases, and a small outbreak in the northwest that has been linked to a traveler from Brazil that has now come under control, demonstrate the challenges that nations face in enforcing travel restrictions as international flights slowly resume.

Spain is trying to host tourists again after a 3-month hiatus as it tries to recover from one of Europe's worst coronavirus outbreaks. Spain has recorded more 28,300 coronavirus-related deaths.

Also, in the northern Aragon region, over 80,000 people face new restrictions after an outbreak linked to a local fruit distribution factory. With 133 infected people isolated, the region’s authorities have declared the cluster “under control.”