U.S. President Barack Obama has told Latin American leaders that the days when his country could freely interfere in regional affairs are past, BBC News report.

He was speaking just before the seventh Summit of the Americas in Panama City.

Obama and Cuban leader Raul Castro shook hands as the opening ceremony began, their first encounter since a December detente. But their historic formal talks due on Saturday could be overshadowed by tensions between Venezuela and the U.S. .

Obama told a forum of civil society leaders in Panama City that "the days in which our agenda in this hemisphere presumed that the United States could meddle with impunity, those days are past".

At past Summits of the Americas, which bring together the leaders of North, Central and South America, the U.S. has come in for criticism for its embargo against Cuba and its objection to having Cuba participate in the gatherings.

This seventh summit is the first which Cuba will attend.

Barack Obama and Raul Castro are due to meet again later on Saturday. It will be the first formal encounter between the leaders of the U.S. and Communist-run Cuba in more than five decades.

Before the summit began, the U.S. president stressed that he hoped the thaw in relations would improve the lives of the Cuban people.