Washington (AFP) - Secretary of State Mike Pompeo warned Russia Monday the United States will not "stand idly by" as Moscow inserts military personnel into Venezuela to support the regime of President Nicolas Maduro.

In a phone call with Foreign Minister Sergei Lavrov, Pompeo denounced the growing Russian military reinforcements as prolonging the political crisis in the South American country.

Pompeo told Lavrov "the United States and regional countries will not stand idly by as Russia exacerbates tensions in Venezuela," the State Department said in a statement.

"The continued insertion of Russian military personnel to support the illegitimate regime of Nicolas Maduro in Venezuela risks prolonging the suffering of the Venezuelan people who overwhelmingly support interim President Juan Guaido," he said.

Guaido is supported by the United States and most Latin American and European nations but Maduro retains the support of Russia and China, US rivals who have offered political and economic support to him.

Pompeo urged Russia to "cease its unconstructive behavior" and support Guaido.