NICOSIA (AP) ― Hundreds of angry marchers forced their way into the grounds of the Cypriot presidential palace in Nicosia late Tuesday, during a protest over a fatal blast at a naval base that killed 12, wrecked a key power plant and forced the resignations of the defense minister and top military chief.

Protesters chanting “the people demand that the murderers are thrown in jail” were stopped at an inner gate about 100 meters from the palace by riot police.

Police fired volleys of tear gas after being attacked by a group of stone-throwing youths who crowded a palace exit. Youths later set fire to rubbish bins outside the palace grounds. Police made several arrests, but no injuries were reported.

It was unclear whether President Dimitris Christofias was in the building.

Monday’s massive explosion leveled Evangelos Florakis base south of Nicosia, turning fire trucks and military vehicles into twisted piles of scrap and shooting shards of copper and steel over a wide area. Many parts of the island are still intermittently without electricity after the powerful concussion wave knocked out the main power station.

The island’s Navy Chief and the base commander were among the dead.

Government spokesman Stefanos Stefanou said Greek experts have already joined Cyprus police and military investigators in scouring the rubble for clues while French officials were en route. Authorities have ruled out sabotage.

The probe comes amid a torrent of criticism over how the 100 containers ― most of them filled with gunpowder ― had been stored.

Tuesday’s invasion, unprecedented in a country where violent political protests are rare, followed a peaceful march by some 10,000 people shouting slogans and carrying placards reading “Negligence is criminal.”

The protest was organized online, and spread through social media and mobile phone text messages.

“We’re here to protest the irresponsibility of our government,” said protester Nectaria Mihail, 30. “All (officials) care about is their cushy positions and money, they should be ashamed of themselves.”

The containers had been stacked one on top of the other in an open field at the navy base since 2009, when they were seized from the Cypriot-flagged M/V Monchegorsk that the United Nations said was breaching a ban on arms exports.

Military officials had previously expressed fears of what exposure to the elements would have on the containers and the gunpowder in letters to the Defense Ministry. Cyprus Auditor General Chrystalla Georghadji was quoted in an annual report in 2009 as saying that the contents’ “composition and reaction to high temperatures is unknown.”

“There will be an in-depth investigation, all will be investigated thoroughly and responsibility will be apportioned where it is due,” Stefanou told reporters, adding that President Christofias had not been briefed on the containers’ storage conditions or of any dangers relating to the gunpowder.

Stefanou said the government had sought to transport the containers to either Malta or Germany, but received no reply from the U.N. Security Council whose authorization he said was needed to do so.

Fotis Fotiou, a spokesman for the governing coalition, center-right party DIKO said “it is obvious that criminal negligence” caused the “national tragedy.”

“There must be punishment,” he said.

In a written statement issued late Tuesday, Stefanou said a police-led criminal investigation into the blast will run concurrently with another probe to be carried out by a committee Christofias will appoint to swiftly examine “all aspects of the issue and apportion whichever responsibility.”

The powerful concussion wave also smashed window panes, tore off roof tiles and blew in doors to more than 240 homes in communities within a five-kilometer radius of the naval base.

Two men injured in the blast remain in critical condition. Nicosia General Hospital official Theodoros Kyprianou said one of the two men ― a soldier ― “had no face or eyes” and that his mother initially recognized him from a mark on his hand.

Health Minister Christos Patsalides said Israeli doctors would arrive on the island to assist Cypriot colleagues in treating the injured.

Rolling two-hour power cuts were in effect island-wide Tuesday as officials said it will take months before the power station ― which provides more than half the island’s power demand ― is brought back fully online.