* Navy vessel helps capture Somali pirates
* Pirates targeting expatriate workers
By Fumbuka Ng'wanakilala
DAR ES SALAAM, Oct 4 (Reuters) - Tanzania has arrested seven suspected Somali pirates after an attack on an oil and gas exploration ship operated by Brazilian petroleum company Petrobras off the coast of the east African country.
The incident followed the separate abductions of two Western women in neighbouring Kenya in less than one month. The kidnappers escaped by speedboat to Somalia's southern rebel-controlled tip that borders Kenya's northern border.
"The Maritime Rescue Coordination Centre (MRCC) ... has received reports of an attack on an exploration vessel known as the Ocean Rig Poseidon," Tanzania's Registrar of Ships said in a statement on Tuesday.
"In the incident, seven pirates in a small boat attacked the ship with weapons. Security personnel on the ship with the help of the Tanzanian navy returned fire and managed to subdue and arrest the pirates."
The incident, which officials said occurred late on Monday about 82 nautical miles from the capital Dar es Salaam, brings to 18 the total number of pirates arrested in Tanzania following attacks in its Indian Ocean territorial waters.
Tanzania in April ordered its army to escort ships searching for oil and gas off its coast to protect them from Somali pirates, who are suspected of kidnapping expatriate workers on exploration ships for hefty ransoms.
Analysts had warned Somali pirates were likely to turn to softer targets, such as tourists in Kenya, in response to more robust defense of merchant vessels by private security guards.
Somalia's al Shabaab militants have also escalated their attacks in the lawless Horn of Africa nation, killing at least 70 people in an attack in Mogadishu on Tuesday.
Petrobras has a production sharing agreement licence for Block 5 and 6 deep offshore basin off Tanzania and launched the Poseidon ship's exploration work in Mtwara, southeast of Tanzania, in September.
The Brazilian firm, which has invested $11 million in Tanzania, and plans to spend another $14 million to develop Mtwara port, said the ship would carry out exploration for a duration of 20 months.
The East African country has licensed at least 17 international companies to look for offshore and onshore energy reserves.
(Reporting by Fumbuka Ng'wanakilala; Editing by Yara Bayoumy)