Nigeria has declined to approve the sale of Shell's (NYSE:SHEL) onshore and shallow-water oil and gas in the Niger Delta region to a consortium of local companies, the country's upstream regulator said Monday.

"We estimate that approximately 30-40 metric tonnes of slop, which is a mixture of oil and water, was leaked into the sea," the company said in a statement, adding that it was working with all relevant authorities to manage the clean-up effort.

Singapore said it was alerted to an oil leakage from a Shell land-based pipeline early Sunday, and steps have been taken to clean up the spill.

A land-based pipeline leak has led to about 30-40 metric tons of "slop” - a mixture of oil and water - being spilled into the sea off Singapore, Shell Plc said in a statement today.

Major energy company Shell and Singapore's Maritime and Port Authority deployed clean-up measures after a leak from a land-based pipeline, they said on Sunday.

An oil leakage from a pipeline in Singapore operated by Shell (NYSE:SHEL) was reported early Sunday, according to local officials. They said a cleanup was under way. The leak was reported to have “stopped at source,

An oil pipeline belonging to British giant Shell began leaking into the sea on Sunday, Singaporean authorities said, adding that the spill was stopped and cleanup crews deployed.