Bolivia blamed the United States on Tuesday for cooking up an influence-peddling scandal that has embarrassed the president by disrupting multimillion-dollar trade deals by Chinese companies.

President Evo Morales has said he is considering expelling the top US diplomat in the South American country, Peter Brennan, over the affair.

The scandal has seen Morales' opponents accuse him of influence-peddling linked to Chinese construction firm CAMC, where his ex-girlfriend holds a top post.

CAMC signed contracts worth at least $560 million with Morales' government.

"What people are trying to do is discredit Chinese investment in Bolivia and Latin America. This is a treacherous attack by the United States against Bolivia," minister of the presidency Juan Ramon Quintana said, alleging that Washington was lashing out at Morales' leftist policies.

Quintana suggested Brennan had fed the corruption story to a Bolivian journalist.

Morales has overseen robust economic growth but opponents accuse him of presiding over corruption and investing in flashy infrastructure projects at the expense of health and education.

He has won the past three presidential elections. On Sunday Bolivians will vote in a referendum on a constitutional reform that could allow Morales to be re-elected until 2025.