Bahrain Mirror (AP): Bahraini police announced Wednesday they seized 1.5 tons of explosives in a warehouse and underground bunker system south of the capital, Manama, in one of the largest such busts amid ongoing unrest in the tiny island kingdom.

The material seized in the Nuwaidrat residential district, including C4, RDX and TNT, as well as hand grenades, matched explosive traces found at a series of recent attacks in Bahrain, the Interior Ministry said, without elaborating. Police said in a statement they made "a number" of arrests, claiming those suspected of being involved had ties to Iran and the Shiite militant group Hezbollah.

"This significant discovery marks yet another disturbing incident in which relentless Iranian actions are attempting to undermine security and stability within Bahrain and the wider region," police Maj. Gen. Tariq Al Hassan said. "The sophistication of terrorist-related incidents in Bahrain has increased markedly during 2015, and the professionalism with which these materials are manufactured, concealed and deployed is a clear indication of international support and sponsorship."

Iranian officials could not be immediately reached early Thursday morning. They previously have denied being involved in attacks in Bahrain.

Bahrain has faced low-level unrest for more than four years, sparked by widespread 2011 protests among the country's Shiite majority demanding greater political rights from the Sunni-led monarchy.

In July, a bombing killed two police officers and wounded six in Sitra, south of Manama. Police investigators say five suspects arrested for that attack are connected to Iran's Revolutionary Guard, as well as the Iranian-backed Lebanese Hezbollah group. Police said a "terrorist blast" in late August killed one police officer and wounded six people.

Bahrain hosts the U.S. Navy's 5th Fleet.