MANAMA (REUTERS) - Bahraini authorities have foiled an attempt to smuggle explosives and arms, some made in Iran and Syria, into the country by boat, the Gulf Arab state's public security chief said on Monday.

Bahrain, home to the US Fifth Fleet, has been rattled by bouts of unrest since February 2011, when protests led by members of its Shi'ite majority demanded that the Sunni ruling family give up ultimate power to an elected parliament.

"According to the investigations, which revealed plans to carry out terrorist acts, security deployment has been intensified," Major-General Tariq al-Hassan said in comments published by the official news agency BNA.

He said security forces had also dismantled a car bomb in the al-Houra area east of Manama, seized a weapons and explosive cache and arrested 13 people, including a Saudi Arabian national, trying to flee the country by boat.

The smuggled munitions included what Hassan called anti-personnel and armour-piercing explosives, as well as "50 Iranian-made hand bombs" and "295 commercial detonators on which was written 'made in Syria'", he said.

The Manama government, dominated for generations by the Sunni Muslim Al Khalifa family, accuses the opposition of having a Shi'ite sectarian agenda and links to Iran and to Lebanese Shi'ite militant group Hezbollah.

The opposition denies this, saying such allegations are a pretext for avoiding democratic reforms. Tehran also denies any link, but champions the cause of the opposition while Hezbollah has criticised Manama's crackdown on Shi'ite protesters.

The Bahraini government largely put down the uprising with help from Gulf Arab neighbours but small-scale clashes continue and bomb attacks mainly on policemen and security officers have been increasing since mid-2012.

Bahrain's Shi'ite opposition groups suspended their participation in reconciliation talks with the government after the arrest of a senior member of al-Wefaq, the main opposition group, in September.