Royal Dutch Shell's Nigerian venture has shut in a number of oil installations after explosions on a pipeline that may have been due to sabotage, a company spokeswoman said on Tuesday.

The blasts caused at least three punctures to the 24-inch trans-Escravos pipeline, which sends crude oil to the Escravos oil export terminal in Nigeria's Niger Delta.

Shell officials declined to say how much production was affected by the damaged pipeline, first reported by a surveillance team on Saturday. News of the disruption in Africa's top oil producer helped push global oil prices higher.

"SPDC can confirm that there have been explosions on the trans-Escravos pipeline," said Shell spokeswoman Kirsten Smart. "A number of facilities have been shut in to minimize potential damage to the environment."

"The indication is that the damage is the result of sabotage acts, but there's an ongoing investigation that is looking into it."

Shell said it was not aware of any injuries or deaths caused by the explosions.

Violence in the Niger Delta, the heart of Nigeria's oil and gas sector, has cut a fifth of the OPEC member's production in the last three years.

Nigeria's most prominent militant group, the Movement for the Emancipation of the Niger Delta (MEND), called off a ceasefire a month ago. But it has not claimed any significant strikes against the industry, partly because the military has stepped up a campaign to flush out its fighters.

U.S. crude oil was up 60 cents at $40.75 as of 1525 GMT.