(Adds one source says Nigerian crew captured, paragraphs 3-4) LAGOS, March 12 (Reuters) - Gunmen in speedboats captured a a barge carrying building materials through the creeks of the Niger Delta in southern Nigeria, where piracy is one of several threats to the oil industry, security sources said on Wednesday. They said the barge and its tug, operated by Nigerian-German construction group Julius Berger, were on their way to the delta's main city of Port Harcourt when the attackers struck. One of the security sources said that five Nigerian crew were being held hostage by the attackers who were demanding a 20 million naira ($170,000) ransom. This could not be confirmed from any other source. The Niger Delta, home to Africa's biggest oil industry which exports about 2.1 million barrels per day, is plagued by militancy and crime. Piracy, abductions for ransom, armed robberies and crude oil smuggling are all common problems. Attacks on oil industry vessels and other commercial ships have become increasingly frequent over the past two years, prompting seamen's unions to campaign for shipping firms to grant crew war-risk bonuses for operating in Nigerian waters. Julius Berger, an arm of German firm Bilfinger Berger AG <GBFG.DE>, is the biggest construction group in Nigeria. It is upgrading the delta's main east-west road linking the oil industry hubs of Port Harcourt and Warri. A German man working for the firm was kidnapped for 12 hours on March 4 and released unharmed, in the first abduction of a foreigner in the delta for four months. Before the lull, more than 200 foreigners were kidnapped since early 2006. Thousands of expatriate workers and their relatives have been evacuated from the delta since the wave of violence began. Those who remain live under tight security, and ransom seekers have increasingly targeted affluent Nigerians. (Reporting by Estelle Shirbon)
