LAGOS, Nigeria, (AP) – Saboteurs bombed a water pipeline to a government-owned oil refinery in southern Nigeria overnight, according to a military official who said Saturday the attack had not affected production.

Brig. Gen. Alfred Ilogho said dynamite had been placed under a water pipe leading to a refinery in Warri, a town in Nigeria’s southern Delta state.

Residents in the area reported hearing a large explosion around midnight.

The attack comes at the end of a week of violent strikes against petroleum companies in Africa’s largest oil producer. Militants detonated two car bombs on Monday at oil company compounds in the oil-producing hub of Port Harcourt.

On Thursday, armed men raided a Total SA pumping station in an attack that left three police guards dead, while another group took over an Eni SpA facility. The companies shut down production at both facilities, suspending about 80,000 barrels per day in all.

Nigeria has seen its typical oil production of 2.5 million barrels per day cut by a quarter this year by a series of attacks and hostage-takings by militants — some seeking ransoms and others political influence.

Gangs and politically minded militants say attacking the oil infrastructure is the only way for them to get a share of the country’s oil wealth.

In a sign that the security situation could be worsening, Royal Dutch Shell PLC began evacuating all dependents of foreign employees from the delta region this week, citing the deteriorating security situation following the car bombs — one of which was set off in a Shell complex.