* Frequency and fatality of bomb attacks on rise
* Videos show training of Shi'ite youth, assaults on police
* Attacks often outside capital but fears linger
* Reconciliation talks "frozen", opposition says
* Bahrain is strategic linchpin for U.S. against Iran
By Rania El Gamal
MANAMA, May 4 (Reuters) - Dozens of black-clad, masked men parade through Bahrain's Shi'ite Muslim villages, some holding petrol bombs and others denouncing al Khalifa, the Sunni Muslim monarchy that has ruled the Gulf Arab island since the 18th century.
A few masked men jump through a ring of fire and crawl under barbed wire in what looks like a desert training zone. Hands work at what looks like a home-made bomb.
Scenes like these, broadcast in online videos in recent months, might once have been dismissed as a cry for attention by groups from Bahrain's big Shi'ite community seeking to shore up a flagging cause for democratic reform. But they have coincided with a spread in sometimes lethal home-made bomb attacks, suggesting a growing radicalisation among Shi'ite youth.
To be sure, the parades do not match either in size or armed might those of paramilitary Shi'ite militias elsewhere in the Middle East such as Lebanon's Hezbollah or Iraq's Mehdi Army. Nor do the bombs disturb everyday life in most of Bahrain, where explosions tend to target security forces in the mainly Shi'ite villages, far away from the capital.
But there are fears that a deadlock in political efforts to solve a three-year-old standoff is deepening frustration among young Shi'ites, with the more hotheaded of them seeming beyond the control of the mainstream al Wefaq opposition movement.
"We are fighting for our rights and nobody can stop us. The youngsters will continue what their fathers, brothers and uncles started," a 21-year-old man who gave his name only as S. A. told Reuters in the Shi'ite village of Janabiya. "Many of us have lost a member of the family; that has became a norm. But we are fighting back and will kill whoever is killing us."
The strategically vital kingdom, which hosts the U.S. Fifth Fleet, has wrestled with low-level but persistent civil unrest since a Shi'ite-led uprising was put down in 2011, becoming a front line in a region-wide tussle for influence between Sunni Saudi Arabia and Shi'ite Iran across the Gulf.
Many of the youth in the videos hold the flag of the February 14th Youth Coalition, an internet-based group that has been organising anti-government protests since security forces quelled mass demonstrations of February-March 2011, inspired by the "Arab Spring" wave of popular revolts against autocracy.
February 14th, named after the launch date of the 2011 uprising, has been declared a terrorist organisation by the authorities along with two little-known groups: Saraya al-Ashtar (Ashtar Brigade) and Saraya al-Muqawama (Resistance Brigade), compounding the atmosphere of confrontation.
Demonstrators drawn mainly from the Shi'ite community have kept up small protests almost daily, demanding the Sunni ruling family create a constitutional monarchy.
Some of the protests turn violent, with police firing tear gas, stun grenade and birdshot at youth burning tyres and throwing rocks, metal rods and petrol bombs at security forces.
The violence is mainly in Shi'ite villages well away from Manama where businesses and expatriates are hardly affected.
Yet, there is a risk of a deadly attack that could plunge Bahrain into a more brutal cycle of violence. Tension simmers with no solution for the grievances cited by the Shi'ite community, particularly the youth many of whom say they have members of their families either shot by police or in jail.
Bahraini Shi'ites complain of political and economic marginalisation, an accusation the government denies.
Justin Gengler, a Bahrain expert at Qatar University, says the risk of youth radicalisation is "a predictable consequence".
"When a large segment of the population feels that so-called 'representative' institutions are stacked against them, and that no viable avenue of reform exists, then it is not surprising that they would turn to extra-political means of affecting change," he said.
"The unrest is contained, it is managed to a great extent," said a Western diplomat, who asked for anonymity.
"But there is a sense, I think, that if they don't come to a political solution, it could be a big event that would set it off, and it could develop into sectarian (violence). It is one of the greatest fears."
Diplomatic and security sources in Manama cite increasing evidence of Iranian support for some "violent" anti-government groups in Bahrain. They point to a foiled attempt to smuggle explosives and arms, some made in Iran and Syria, into the country by boat last year.
"The evidence is irrefutable, the Iranians are involved," said the Western diplomat, who added that groups behind the attacks were getting better in making deadly explosives.
Iran has always denied accusations of fuelling the unrest, yet it champions the cause of Bahrain's Shi'ite opposition.
VIDEO OF BOMB ATTACKS
The online videos include footage purportedly of some of the bomb attacks that have killed or wounded policemen in recent months. In one video, masked youths run with petrol bombs which they throw at an armoured police vehicle. The car, on fire, drives away and the youth shout "Allah Akbar" (God is great).
Parts of Hezbollah chief Sayyed Hassan Nasrallah's speeches, or songs calling to "answer the call of the Coalition", are sometimes played in the background of other videos.
Reuters could not independently verify the videos. Some commentators have pointed out that they could have been made by government loyalists to mobilise support for the authorities.
Yet analysts, security and diplomatic sources say the recent spike in the frequency and deadliness of bombing attacks, mainly on policemen, indicate a greater level of experience and training by the attackers than two years ago.
Mohammed al-Sayed of Citizens for Bahrain, which identifies itself as an online moderate movement, said there is growing concern that radicals from both Sunni and Shi'ite communities are gaining ground. "If it's policemen today, then it's civilians tomorrow that would be targeted," he said.
"Another main concern among Bahrainis is that children are being exploited. They are blocking roads, burning tyres and even carrying bombs in some areas. If this is what we will be facing in the future of Bahrain's youth, what will happen in 10 or 20 years and how polarised and radicalised would they become?"
During this year's Formula One Grand Prix race, a home-made bomb exploded in a car in a busy commercial district of Manama.
No casualties were reported and the F1 race was unaffected. But the blast took place near a government security building, despite tight security around the country because of the race, raising fears of possible high-profile attacks.
A meeting between Bahrain's crown prince and opposition leaders in January pulled reconciliation talks back from the brink of collapse but mutual mistrust runs deep. Little progress has been made since and the opposition said talks were "frozen".
"The political crisis is deep and will not be solved with superficial talks that aim to waste time and continue human rights violations," opposition groups said in a statement last week. Information Minister Samira Rajab said on April 27 the talks were continuing, according to state news agency BNA.
"It is a political game," said a Wefaq member who asked not to be named. "They want to pressure the opposition to negotiate and lessen their demands. But we worry that the more violent the authorities become, the more violent the people will also become." (Additional reporting by Farishta Saeed; Writing by Rania El Gamal; Editing by William Maclean and Mark Heinrich)