July 4 (Reuters) - Gunmen attacked an oil drilling rig and kidnapped five expatriates in the Niger Delta in southern Nigeria on Wednesday, dealing a blow to a fledgling peace process in Africa's oil heartland.

Below is a chronology of some major attacks and kidnappings involving the Nigerian oil industry in the past two months.

-- May 3 - Gunmen kidnap 20 foreign workers in three attacks in the Niger Delta, but eight are freed within hours.

-- May 5 - Gunmen abduct a British oil worker from Trident 8 rig operated by U.S.-based Transocean off the coast of Bayelsa. Separately, gunmen abduct a Belarussian woman, a manager of Britain's Compass Group, from outside her home in Port Harcourt's exclusive GRA district. She is freed on May 16.

-- May 8 - Three South Koreans and eight Filipinos are freed after being held for five days.

-- Rebels blow up three oil pipelines in the Niger Delta, forcing Eni to halt production of 150,000 barrels per day feeding its Brass export terminal. The Movement for the Emancipation of the Niger Delta claims responsibility.

-- May 19 - Two Indian staff of Eleme Petrochemical Company, majority-owned by Indonesia's Indorama, are kidnapped by gunmen in Port Harcourt.

-- May 22 - Four gunmen kidnap a Lebanese man who is a financial controller at oil service company Nigercat in Warri.

-- May 24 - Gunmen kidnap a Polish engineer near Warri. He is released on May 28.

-- May 25 - Nine oil workers are kidnapped from a ship off the Nigerian coast; those held are three Americans, four Britons. A South African and a Filipino are released on June 11.

-- May 30 - Four U.S. oil workers, kidnapped on May 9 from a barge off the coast near Chevron's Escravos crude export terminal, are freed.

-- June 3 - Gunmen kidnap six staff of United Company RUSAL, the Russian aluminium giant, in Ikot Abasi in the southeast. The men were working at the Aluminium Smelter Company of Nigeria.

-- June 11 - Five Britons and three Americans are released in Bayelsa state. Two Indians are also freed.

-- June 15 - Gunmen kidnap two Lebanese men, working for Italian firm Stabilini, near Ogara in Delta state.

-- June 16 - Militants release 10 Indian hostages held since June 1. The hostages included at least three senior executives of Indonesian petrochemical company Indorama.

-- June 21 - Troops kill 12 militants and free some hostages in a dawn raid on an Italian-operated Ogbainbiri oil facility.

-- June 23 - Four hostages, from Britain, France, the Netherlands and Pakistan, employed by oil services giant Schlumberger are released unharmed. The men were abducted on June 1 from Port Harcourt.

-- June 25 - Two Indian construction workers, kidnapped near Sapele in Delta State on June 15, are freed.

-- July 4 - Armed men attack a Shell facility at Soku and abduct five expatriates, two from New Zealand, one Australian, one Venezuelan and one from Lebanon.

AlertNet news is provided by