While Somalia has seen a decline in hijackings in recent months, incidents are on the rise in west Africa

Piracy in west Africa is reaching dangerous proportions, the global piracy watchdog has said, with the increase in attacks fuelled by Nigerian criminals.

As efforts continue to rescue seven foreign workers kidnapped from a vessel off the coast of Nigeria earlier this week, the director of the international maritime bureau (IMB) warned that the region was now a major focal point for armed robberies at sea, and criticised the lack of efforts by governments in the region to tackle the problem.

While Somalia has recorded a decline in hijackings in recent months, incidents are on the rise in west Africa, with 32 reported by July this year. There were 25 in 2011. In Nigeria alone there were 17 reports, compared with six in 2011, with particularly high levels of violence against crew members by pirates armed with guns.

"Piracy in west Africa is a serious problem," said Pottengal Mukundan, IMB director. "Pirates are getting quite audacious, with increasing levels of violence being used.

"These attacks started off the coast of Nigeria, although they have also now spilled over into neighbouring countries. The problem has been there for a long time and authorities have had ample notice to deal with the problem. There is really no excuse for the fact that they have not been able to deal with it."

The warning comes as seven foreigners working for French oil transport company Bourbon were kidnapped while boarding a vessel belonging to the company on Nigeria's Pennington river earlier this week.

A statement on the company's website said that six Russians and one Estonian employed as crew members by the company were being held captive, and that efforts were underway to obtain their release.

"The emergency unit set up immediately by Bourbon has been set up to aim at their rapid liberation under the safest security conditions," the statement said. "Bourbon is in contact with the crew members' families, supporting them, and keeping them regularly informed."

A spokesman for Nigeria's Joint Military Task Force told the Guardian that joint military-naval operations were underway to catch the attackers, and confirmed that incidents of kidnapping and piracy were on the increase.

"The Bourbon vessel that was conveying the expatriates during the incidents has been recovered. We have forward operational bases in the Niger Delta and our maritime friends are at the moment conducting a search to track down the kidnappers. We are conducting a lot of intelligence gathering" said Lt Col Oyeama Nwachukwu.

Although the legal definition of piracy encompasses acts of violence on the high seas, rather than in territorial waters, the incident is one of a growing number linking thieves in Nigeria's Niger Delta, where hundreds of thousands of barrels of oil are stolen from pipelines each day, to increasingly bold attacks on ships.

There are concerns that piracy in and around Nigeria could engulf the entire west African coastal region – known as the Gulf of Guinea – an increasingly busy maritime region and a major thoroughfare for valuable commodities such as oil, gold, bauxite and iron ore, and agricultural products.

Although Nigeria's navy is regarded as relatively successful at tackling piracy off its own shores, experts say the problem has been pushed outwards to neighbouring countries who have little capacity for maritime law enforcement.

Benin and Cameroon have both reported rises in piracy attacks, which experts attribute to Nigerian pirates.

Benin – which depends on its port for around 40% of income – has asked the UN to send an international force to help police the coast in the region. Since being labelled a high-risk country by London-based marine insurers' group the Joint War Committee, the country has suffered a 70% fall in shipping resulting in an estimated £50m ($81m) loss in customs revenue, according to a recent UN report.

The problem has led to calls for a regional taskforce and outside intervention to rival the Nato and EU-led efforts off the coast of Somalia.

The US military said it was stepping up attempts to create a regional taskforce to deal with the problem of piracy in the Gulf of Guinea.

"In the past, most of our efforts have been bilateral," US Africa Command head of air and maritime programmes told Reuters. "Now we are focusing on a regional basis because the solution in regional. Events are picking up in Benin and Togo because Nigeria is stepping up its enforcement efforts."

France has also bolstered surveillance in the region, with reports that the French military will conduct anti-piracy training in Benin and Togo later this year.

"This is a crime which easily spills over across borders, therefore there is a great need for co-operation and information sharing between the countries, but so far in west Africa that cooperation appears to be patchy" said Mukundan.