* Police block people trying to reach prayers
* Boy hit by car, opposition say he was running from police (Adds interior ministry, information affairs authority statements)
MANAMA, Nov 9 (Reuters) - Police in Bahrain fired teargas and blocked roads on Friday to stop thousands of Shi'ite Muslims joining prayers led by one of their spiritual leaders, witnesses said, amid deepening tensions in the Gulf Arab kingdom and U.S. ally.
The island country hosts the U.S. Fifth Fleet and has been volatile since majority Shi'ite Muslims began protesting last year against what they said was widespread discrimination, a charge the Sunni-led government denies.
Shi'ite leaders had called for people to turn out in support of Sheikh Issa Qassim in his village of Diraz, west of the capital Manama, after the government warned clerics not to criticise the government or incite violence.
The call for mass prayers appeared to flout a ban on rallies and protests announced by the interior ministry last month.
An Interior Ministry statement carried on the official BNA news agency said security measures had been taken to "prevent those who were trying to exploit prayers to provoke hooliganism ... and violate freedom of expression".
A statement issued by the government's Information Affairs Authority in English said police had turned away worshippers because the Diraz mosque only accommodated a few hundred people.
Witnesses said some arrests were made as riot police prevented non-residents from reaching Diraz, blocking off all roads and highways.
A 16-year-old Bahraini was killed on Friday on a highway not far from Diraz in what the Interior Ministry said was a traffic accident. Opposition and human rights activists said he had ran onto a busy road while being chased by police.
"Confirmed from several eyewitnesses: Ali Radhi was chased by riot police. He went onto the highway to run away, was hit by a civilian car. We hold the Ministry of Interior responsible for his death," Maryam al-Khawaja, acting head of the Bahrain Centre for Human Rights, said on her Twitter account.
Footage posted on YouTube that could not be independently verified showed a teargas canister going off inside a car carrying women who activists said were on their way to the prayers.
One woman was seen collapsing on the ground after exiting the vehicle.
Last year's Shi'ite-led protests were initially crushed by the kingdom's Sunni Muslim monarchy, with martial law and help from Gulf neighbours.
But smaller demonstrations have since resumed and anti-government protesters clash with security forces several times a week.
The violence has intensified in recent weeks. On Monday, the government said five home-made bombs killed two people in Manama.
The government accused Lebanese militant group Hezbollah of being behind the attacks. Hezbollah, a Shi'ite group allied with Iran, has previously denied interfering in Bahrain.
Bahrain's government said on Wednesday it had revoked the nationality of 31 men for damaging national security, including leading dissidents, parliamentarians, clerics and human rights lawyers. (Writing by Raissa Kasolowsky; Editing by Andrew Osborn)