Preliminary deals South Africa struck with several countries to build new nuclear power stations are "unconstitutional and unlawful," a court ruled on Wednesday.

The High Court in Cape Town ruled that the government failed to adequately consult the public and conduct proper environmental and financial assessments for Russia, South Korea and the United States to build eight nuclear power plants.

Two environmental groups challenged the deals in 2015, arguing the government did not follow proper decision-making procedures. Critics of the nuclear expansion, which was expected to run up to 80 billion euros ($73 billion), said it would be prone to graft.

South Africa has struggled with blackouts for years amid growing demand for electricity. The country has one nuclear plant and gets more than 90 percent of its power from coal.

The government argued the new plants would increase power from nuclear by fivefold.

One of the deals involved strategic cooperation with Russian state nuclear company Rosatom.

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cw/sms (AFP, AP, dpa)