Uganda has granted environmental approval for a $3.5 billion pipeline to export crude oil from western fields to the Indian Ocean coast in Tanzania, despite pressure from lobby groups.

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The planned East Africa Crude Oil Pipeline (EACOP), from fields co-owned by France's Total and China's CNOOC International, would cross sensitive ecological systems including wildlife-rich areas, rivers and swampland that are catchments for Lake Victoria.

International and local environmental groups including Global Witness say it poses unacceptable risks.

But in a statement late on Thursday, Uganda's state-run National Environment Management Authority (NEMA) said it had issued a certificate of approval for the environmental and social impact assessment report submitted by Total.

Dickens Kamugisha, head of the Kampala-based Africa Institute for Energy Governance, said there was insufficient public consultation and his advocacy group would challenge NEMA's ruling in court.

"This is a project that is going to cross dozens of swamps and other fragile ecological areas that are already being stressed by the impact of climate change," he told Reuters.

The 1445-kilometre (900-mile) pipeline, which will run to Tanga port in Tanzania, is key to landlocked Uganda's start of commercial oil production.

Uganda discovered oil in the Albertine rift basin in 2006 but production has been repeatedly snagged by disagreements with foreign oil companies over taxes and development strategy.

State geologists estimate reserves at 6 billion barrels.

President Yoweri Museveni's government has indicated production will start at the earliest in 2022.

As Tanzania had already given its approval, the Ugandan stamp means the project now has environmental impact certification for its entire length.

NEMA's executive director Tom Okurut said the environmental authority would keenly monitor construction to ensure the health and safety of the communities, workers and environment.