MANAMA (Reuters) - Bahraini police fired tear gas and blocked roads to stop thousands of Shi'ite Muslims joining prayers led by one of their spiritual leaders on Friday, witnesses said, amid worsening strife in the Gulf Arab kingdom and U.S. ally.

The island country has been volatile since majority Shi'ite Muslims began protesting last year against what they say is widespread discrimination, a charge the Sunni-led government denies.

Shi'ite leaders had called for people to turn out to support Sheikh Issa Qassim in his village of Diraz, west of the capital Manama, after the government warned clerics not to criticize the government or incite violence.

Bahraini authorities were not immediately available to comment on Friday. But the call for mass prayers appeared to flout a ban on rallies and protests announced by the interior ministry last month.

Riot police prevented media and non-residents from reaching Diraz on Friday morning, blocking off all roads and highways. Some arrests were made, witnesses said.

Footage posted on YouTube that could not be independently verified showed a tear gas 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 escaping from the vehicle.

The protests led by Shi'ites last year were initially crushed by the kingdom's Sunni Muslim monarchy, with martial law and help from Gulf neighbors.

Smaller demonstrations have resumed and anti-government protesters clash with security forces several times a week in the small island country.

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 Heavens)