Story highlights Iranian and Thai fishing vessels were among the targets of four attacks this month

Higher security had cut the number of attacks, but they could increase, expert says

(CNN) Somali pirates successfully attacked an Iranian and a Thai fishing vessel over the past 24 hours, although one crew escaped, an anti-piracy expert said.

There were another two unsuccessful attempts this month.

In March, another two vessels, both Iranian, called the Jaber and the Siraj, were captured just off the Somali coast. The crew of the Jaba escaped by overpowering their captors, but the Siraj crew was taken ashore in September. It was the first successful attack in the Gulf of Aden in two years, Steed said.

According to anti-piracy expert John Steed of Oceans Beyond Piracy, which runs a support program to help hostages, the attacks occurred more than 200 nautical miles off Somalia's coastline. The pirates were using small skiffs, a clear indicator of range.

"The attacks are on fishing vessels, which shows because of the high levels of illegal fishing off Somalia, there are lots of potential fishing boat targets. That's what started the Somali piracy problem in the first place," Steed said from Nairobi.

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