Pirates have looted a Marshall Islands-flagged chemical tanker off Togo and hijacked a Maltese oil products tanker off Gabon in recent days amid a sharp escalation in attacks by maritime marauders plaguing the oil-rich Gulf of Guinea off West Africa.

Since 2012, piracy in the Atlantic Ocean off West Africa, one of the hottest oil zones in the world, has outstripped the problem off East Africa, which for the last six years has been the pirates' most troublesome hunting ground, a vast area of sea stretching 1,000 miles into the shipping lanes of the Indian Ocean.

In part this is because security off lawless, war-torn Somalia and the Horn of Africa, the pirates' main operational base, has improved, with international naval task forces, on-board defenses and the rapid growth of a highly lucrative maritime security industry with armed guards on merchant ships, gradually getting the better of the pirate gangs.

Until recently, piracy off West Africa was centered almost exclusively in the Gulf of Guinea and concentrated primarily on oil shipments by Nigeria, Africa's top producer. But as the oil boom spread, the piracy extended to the waters of Togo, Gabon, Benin and the Ivory Coast.

The waters of West Africa are becoming more dangerous to shipping because there's little anti-piracy cooperation between the region's states, who don't have the naval or coast guard forces to protect ships and offshore oil platforms, and the oil boom provides plenty of fat targets, including offshore platforms.

U.S. forces have sought to bolster training and operational deployments but budget cuts and Persian Gulf deployments have limited this effort.

The core of the piracy problem is the presence of high organized criminal organizations and oil-stealing insurgents based in Nigeria, where they've been plundering the country's oil industry for years, costing the Nigerian state an estimated $1 billion a month.

The International Maritime Bureau, which has been monitoring international piracy since 1991, recorded 58 attacks in the Gulf of Guinea during 2012. The toll for 2010 was 33.

But officials say many attacks there aren't reported, usually to prevent insurance premiums being driven up, so that the known incidents reflect only a fraction of the real number that occur.

"This prevents meaningful response by the authorities and endangers other vessels," the IMB reported.

At the same time, it says, there's been a 78 percent drop in the number of ships seizures in the Gulf of Aden and the Indian Ocean in the same period, with a total of 851 mariners attacked compared to 3,863 in 2011.

The IMB, an arm of the International Chamber of Commerce, along with other monitoring groups, reported in June that in 2012 there were for the first time more pirate attacks off West Africa than off the continent's east coast.

But these organizations concluded in a 50-page report that seafarers were in greater danger off West Africa than they were in the east. Five men were killed in pirate attacks in and around the Gulf of Guinea in 2012, with no fatalities reported off Somalia, the report observed.

The west coast pirates are largely involved in stealing oil, sometimes by the shipload, and other cargoes, while those in east mainly held hijacked merchant ships, including fully laden tankers, for ransoms of up to $20 million.

Where hostages are held for an average of four days off West Africa, crews taken by Somali marauders spent an average of 11 months in captivity before ransoms were paid.

"Piracy in West Africa continues to rise slowly, and the constraints placed upon pirates in the east are not nearly as prevalent in the west," the U.S. global security consultancy Stratfor observed.

"Currently there is a dearth of military resources deployed in the Gulf of Guinea."

One of the reasons for the reduction in East African piracy is that in May 2012, EU naval forces finally launched helicopter gunship attacks on pirate bases on the coast, destroying their attack boats.

There doesn't seem to be any prospect of such hard-hitting, counter-piracy operations in the Gulf of Guinea.

"Ultimately, without capable local security forces and foreign naval assets, West African pirates are less constrained than the eastern pirates," Stratfor noted.

"As a result, western piracy will continue to rise -- at least in the short term."