* First time European Union gunships have hit coastline
* EU force uses helicopters and surveillance aircraft
* Pirates hijacked oil tanker last week
By Yara Bayoumy
NAIROBI, May 15 (Reuters) - European helicopter gunships attacked a pirate base on the Somali coast on Tuesday, destroying five speedboats, in the first such airborne strike on land by the anti-piracy force.
The Somali-based pirates responded by threatening to kill crew being held on more than a dozen hijacked vessels if they were attacked again.
The EU Naval Force (EU Navfor) said it had carried out the overnight raid on pirate targets using helicopters and surveillance aircraft with the agreement of the beleagured, Western-backed Somali government.
It was the first time EU Navfor had taken its fight against the pirates to Somali soil since its mandate was expanded earlier this year to allow strikes on land as well as sea.
But at risk are over 300 hostages of various nationalities held by the pirates, who have so far generally refrained from killing crew as they seek multi-million dollar ransoms.
A Somali pirate who identified himself as Abdi told Reuters that a helicopter attacked the central Somali coastline near Hardhere, a known pirate haven.
"An unidentified helicopter destroyed five of our speedboats early in the morning. There were no casualties. We were setting off from the shore when the helicopter attacked us. We ran away without counter-attacking," he said.
"If we are attacked while with hostages, we shall take any necessary step to save ourselves, we may also kill the hostages if we miss other options to survive," Abdi told Reuters.
EU Navfor said it had carried out the attack to destroy pirate equipment, four days after Somali gunmen hijacked a Greek-owned oil tanker carrying close to a million barrels of crude oil in the Arabian Sea.
EU Navfor's Operation Commander, Rear Admiral Duncan Potts, said the attack would "further increase the pressure on, and disrupt, pirates' efforts to get out to sea to attack merchant shipping and dhows".
Somalia's government said it had backed the strike against the pirates, and encouraged further attacks. "(The government) and the EU had agreed upon inland attacks on pirates, avoiding civilian casualties. We were aware of the EU operation today," government spokesman Abdirahman Osman told Reuters.
"We encourage frequent in land attacks - this is the only solution to piracy," he said.
EU Navfor said no Somalis had been wounded as a result of the attack and no EU forces had landed on Somali territory, which has been lawless and torn by armed violence since warlords overthrew dictator Mohamed Siad Barre in 1991.
"We have monitored several locations for quite a long time and the time and place chosen was one of the best opportunities," said Timo Lange, a media officer for EU Navfor.
He said the force would launch similar attacks in future "given that those targets will show up again".
In March the EU extended its counter-piracy operation off the coast of Somalia to the end of 2014 and expanded the area it covers to include the coastline itself.
"The concern is that pirates will simply relocate logistics bases further inland, possibly among coastal communities, to avoid EU airborne attacks," Rory Lamrock, an intelligence analyst with security firm AKE, told Reuters.
"Hostages are still a ransomable commodity and intentional murders will remain unlikely, but an escalation in violence directed at hostages is definitely a possible response."
Despite successful efforts to stop attacks in the Gulf of Aden shipping lane, international navies have struggled to contain piracy in the Indian Ocean and Arabian Sea due to their limited resources and the vast distances involved.
"(It) may take time to limit the overall scope of pirate activities. The pirates have had virtually unconstrained ability to operate for five or six years now and that won't be rolled back rapidly," said a maritime analyst who declined to be named.
The Somali pirates have raked in millions of dollars in ransoms in recent years in what has become a highly organised international criminal enterprise.
A study published earlier this year by the One Earth Future Foundation showed Somali piracy cost the world economy some $7 billion last year, with ransoms paid reaching $160 million.
Somali pirates are switching back to using smaller cargo and fishing vessels as "motherships", hoping to evade detection in the face of more robust maritime security.
The International Transport Workers' Federation, one of the biggest unions representing seafarers, welcomed the EU Navfor attack.
"Limited though the effects of any one single operation can be, it sets a precedent for future actions. It is particularly welcome in a week that has seen increased use of weapons and violence by pirates," said union chairman David Heinde. (Additional reporting by Mohamed Ahmed in Mogadishu and William Maclean and Jonathan Saul in London; Editing by Richard Lough and Mark Heinrich)