Nigeria's President Muhammadu Buhari has pulled out of a visit Thursday to the restive oil-rich Niger delta to launch a pollution clean-up, a presidency official said.

"The presidency has not cancelled the trip to Ogoni but President Buhari will be represented by the Vice-President (Yemi Osinbajo)," the official told AFP.

No reason was given for the sudden change in plan but it comes in the wake of an upsurge in militant attacks on key oil infrastructure in the creeks and swamps of the oil-producing south.

Buhari also pulled out recently of a planned trip to Lagos, which would have been his first trip as president to Nigeria's financial and business hub. Scheduling problems were blamed.

Attacks on pipelines and other infrastructure have cut Nigeria's oil production to some 1.4 million barrels per day, exacerbating revenue shortfalls caused by the global slump in crude prices.

Buhari had been scheduled to visit Ogoniland in Rivers state for a long-awaited clean-up of the region.

In August 2011, a United Nations Environment Programme (UNEP) report said the region may require the world's biggest-ever clean-up after a succession of oil spills.

Oil giant Shell was forced to pay compensation to farmers and fishermen who have lost their livelihood after court action was brought in Britain.

Environmental devastation to farming and fishing in the area has for many come to symbolise the tragedy of Nigeria's vast but squandered oil wealth.

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