By Andrew Cawthorne

CARACAS (Reuters) - Venezuela's foreign minister lambasted U.S. Secretary of State John Kerry on Friday as a "murderer" fomenting unrest that has killed 28 people in the South American OPEC member nation.

Since street demonstrations began against President Nicolas Maduro's socialist government in early February, Venezuelan officials have been accusing Washington of stirring the country's worst political troubles in a decade.

U.S. officials say Venezuela is using them as a scapegoat, inventing accusations to distract from internal economic and political problems. In the sternest words during the crisis from Washington, Kerry said on Thursday the Venezuela government was using a "terror campaign" to repress its own citizens.

"Every time we're about to isolate and reduce the violence, Mr. Kerry comes out with a declaration and immediately the street protests are activated," Foreign Minister Elias Jaua said in a speech carried on state TV.

"Mr. Kerry, we denounce to the whole world, you encourage the violence in Venezuela ... We denounce you as a murderer of the Venezuelan people."

After tense relations during the 14-year rule of the late Hugo Chavez, there had been some hopes on both sides of a rapprochement between Venezuela and the United States.

Kerry and Jaua did actually meet in June last year, on the sidelines of a meeting of the Organization of American States in Guatemala, with both governments saying they wanted better ties.

But the bitterness and incidents have continued, with Maduro last month expelling three U.S. diplomats he accused of recruiting protesters. Washington responded in kind.

"In Guatemala, you said to me 'you have to lower the tone'," Jaua added in his speech. "We are not going to lower the tone to any empire until you order your lackeys in Venezuela to cease the violence against the people."

Despite the harsh words, pragmatism has continued to trump politics when it comes to oil, with shipments unaffected and the United States remaining Venezuela's main export market.

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Elected last year to replace Chavez who died of cancer, former bus driver Maduro has faced six weeks of protests led by militant opposition leaders and students.

As well as the 28 deaths during the unrest, more than 300 people have been injured. Security forces have arrested nearly 1,300 people, of whom about 100 are still in jail.

Maduro says he has seen off a "coup" attempt, and he does not look in danger of being toppled by a "Venezuelan Spring", with the military apparently still behind him.

But opponents and rights groups say he has used heavy-handed tactics against opponents, including unnecessary brutality from troops and police on the street. Several dozen detainees have denounced being beaten and other forms of mistreatment.

A hard core of mainly student protesters are vowing to stay in the streets until Maduro quits.

(Editing by Stephen Powell)