While some Philippine hackers have reportedly launched retaliatory attacks, the government appealed to them for restraint, said Roy Espiritu, spokesman of the government's information technology office.

"We've actually detected several attacks, including attempts at distributed denial of service," he said, in which a hacker infiltrates computers with which to attack a single target, such as a website, forcing it to shut down.

"They (hackers) are probing into different (Philippine) government domains so we can't say how many attacks there are. But it is a lot," Espiritu told AFP.

"The signatures (of the hackers) indicate they are from Chinese networks."

Espiritu conceded this could be a ruse and the attacks may have actually originated from other sources.

But he said all the attacks came after Philippine ships faced off with Chinese patrol vessels in April 8 in the disputed Scarborough Shoal in the South China Sea. Before that, there had been no such attacks.

The Chinese vessels initially prevented the Philippine Navy from arresting alleged Chinese poachers in the area. The stand-off is continuing.

Budget Secretary Florencio Abad said his agency's website had again been defaced on Wednesday, just days after a similar hacking attack.

Earlier, three of President Benigno Aquino's websites and a state university website were also attacked, supposedly by hackers from China.

In at least one case, the hackers left a message asserting China's claim to the South China Sea.

Espiritu said the technology office had implemented its own "firewall procedures" to fend off many of the attacks and was working with law-enforcement agencies to investigate them.

He called for restraint from vengeful local hackers. "We would like to request them to be the bigger man and not escalate the situation."

"Over the past three years, the Iranian regime has invested heavily in both defensive and offensive capabilities in cyberspace," said Ilan Berman, vice president of the American Foreign Policy Council.

"Equally significant, its leaders now increasingly appear to view cyber-warfare as a potential avenue of action against the United States," he told a House Homeland Security subcommittee.

Patrick Meehan, Republican chairman of the committee, also sounded an alarm over the cyber-security threat posed by Iran to western nations.

"As Iran's illicit nuclear program continues to inflame tensions between Tehran and the West, I am struck by the emergence of another possible avenue of attack emanating from Iran -- the possibility that Iran could conduct a cyber attack against the US homeland," he said.

The Republican lawmaker said Tehran has reportedly invested over $1 billion in bolstering cyber capabilities, and is believed by some analysts to be the perpetrator of recent attacks on news organizations.

"Iran is very publicly testing its cyber capabilities in the region and, in time, will expand its reach," Meehan warned.

He added that he has concluded after consultations with US partners in the Middle East that "Iran is the most destructive and malicious actor in the region and will persist in antagonizing the United States and our allies -- especially the state of Israel."

Meehan recalled Senate testimony earlier this year from Director of National Intelligence James Clapper who testified that Iran's intelligence operations against the United States, including cyber capabilities, "have dramatically increased in recent years in depth and complexity."

Experts on the panel said Iran's desire to target the United States could be fueled by a desire for payback after the 2010 Stuxnet worm attack which disabled the Iranian centrifuges used to enrich uranium, dealing a major setback to Iran's nuclear program.

No one has claimed responsibility for the attack although speculation has centered on Israel and the United States.

Stuxnet and similar cyber-attacks allegedly launched against Iran by the West are likely to have steeled its resolve to launch a cyber-assault of its own, experts said.

"For the Iranian regime the conclusion is clear. War with the West, at least on the cyber front, has been joined, and the Iranian regime is mobilizing in response," Berman said.