The United States and Cuba resume talks on Thursday aiming to overcome obstacles to opening embassies in each other's capitals and re-establishing diplomatic ties, the crucial next step in their historic detente.

Both sides have reported progress toward a deal, part of an agreement clinched between US President Barack Obama and Cuban President Raul Castro in December. Once diplomatic relations are restored, the longtime adversaries will work on the more complicated task of normalizing relations.

But Washington wants assurances that its diplomats will have more freedom of movement, while Castro this week reiterated Cuban concerns that dissidents are receiving "illegal" training at the US Interests Section in Havana.