Updated

A South American effort to end a standoff in talks between Venezuela's government and opposition appeared to have stalled Tuesday, while legislation in the U.S. Congress to punish Venezuelan officials for human rights abuses took a step forward.

The foreign ministers of Colombia, Brazil and Ecuador left Caracas after a two-day visit without persuading opponents of President Nicolas Maduro to return to talks aimed at easing the country's political crisis. In a statement issued Tuesday, the diplomats urged both sides to reflect on the next steps and decide on the date for another meeting in the near future.

Opposition leaders pulled out of month-old talks last week to protest mass arrests at anti-government protests.

As a condition for returning to negotiations, they are demanding progress on their proposals, including an amnesty for jailed activists and a non-partisan commission to investigate the 42 deaths tied to anti-government protests that began in February.

The government's "promises aren't enough," Ramon Guillermo Aveledo, executive secretary of the Democratic Unity alliance, said at a news conference Tuesday.

Maduro has accused the opposition of being obstructionist. On Monday, he urged them not to walk away from the negotiating table, saying such a disappointing outcome goes against the wishes of millions of Venezuelans and benefits the country's foreign enemies.

As a breakdown in the talks looks more likely, a bipartisan effort in Washington to impose targeted sanctions on Venezuela advanced in Congress. By a vote of 16-2, the Senate Foreign Relations Committee approved a bill that would direct the Obama administration to impose a visa ban and freeze the assets of Venezuelan officials who committed human rights abuses during the recent wave of unrest.

Sen. Marco Rubio, a Florida Republican who co-sponsored the bill, said he hoped the full Senate would vote on the legislation in a matter of weeks.

A similar bill cleared a House committee earlier this month.

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Associated Press writer Fabiola Sanchez reported this story in Caracas and Luis Alonso Lugo reported from Washington.