US and Cuban officials met Monday in Havana for new talks on restoring diplomatic ties, but their historic rapprochement was strained by tensions over Venezuela.

The top US diplomat for Latin America, Roberta Jacobson, met her Cuban counterpart Josefina Vidal behind closed doors for a third round of talks on normalizing relations, but the atmosphere of reconciliation was marred by protests over Washington's stance on Venezuela.

As Jacobson touched down in the Cuban capital late Sunday, thousands of people attended a concert and rally to "support the Bolivarian (Venezuelan) people and government" in their mounting row with the United States.

US relations with Venezuela, a key Cuban ally, have been on a downward spiral since President Nicolas Maduro accused Washington in February of sponsoring a coup attempt against him -- a claim Washington denies.

After President Barack Obama slapped new sanctions on seven senior Venezuelan officials accused of an opposition crackdown in the wake of the coup allegation, Maduro responded by recalling Venezuela's envoy to Washington and lashing out at the "imperialist elite."

The elected socialist then ordered 10 days of "defensive military exercises" and asked Venezuela's National Assembly to grant him the power to rule by decree on defense and public safety matters -- a request voted through by his legislative majority Sunday.

The row threatens to blight the goodwill Obama cultivated throughout Latin America by moving to restore ties with Cuba.

It has also exposed the gaps that still remain between the United States and Cuba, which has relied heavily on Venezuelan oil money since the collapse of the Soviet Union.

Havana called Obama's new sanctions "arbitrary and aggressive."

A senior State Department official said Washington was "disappointed" with that stance, but that "it will not have an impact on these conversations moving forward."  

- 'Rolling up their sleeves' –

Unlike the previous two rounds of talks held since the historic US-Cuban rapprochement was announced on December 17, no press conference was scheduled for this week's meetings between Jacobson and Vidal, Cuba's top diplomat on US affairs.

State Department spokeswoman Jen Psaki said officials wanted to hash out the nuts and bolts away from the limelight.

"I think their focus is on rolling up their sleeves, and having tough discussions, and getting the work done," she said, adding it was unclear how long the talks would last.

US and Cuban officials contacted by AFP Monday evening were unable to confirm whether discussions would continue Tuesday.

Both sides are trying to iron out remaining issues with an eye on the upcoming Summit of the Americas in Panama on April 10-11.

Obama is due to attend the summit, where Cuba will also participate for the first time.

Obama has said he hopes the two countries can reopen embassies in each other's capitals before the summit.

But the two sides remain at odds on several thorny issues, such as compensation for American property nationalized after the Cuban Revolution, freedom of movement for diplomats and Cuba's removal from the US black list of state sponsors of terror.

And lifting the trade and financial embargo the United States slapped on Cuba in 1962 would require approval from Congress -- a difficult political battle with both houses currently under Republican control.

The two sides are next due to meet in late March, when they will address the delicate issue of human rights for the first time.

The United States severed diplomatic ties with Cuba in 1961 and continued to isolate the country, the only communist regime in the Americas, even after the Cold War ended.