Mainland hackers were likely to be behind an attack on the website of Taiwan's ruling party, a US-based security firm said Thursday, as the island warns of growing cyber threats.

Cross-strait relations have turned increasingly frosty since Taiwan's new president Tsai Ing-wen of the China-sceptic Democratic Progressive Party (DPP) won elections in January and took office last month, with Beijing wary the new government may seek independence.

Taiwan has been self-ruling since the two sides split in 1949 after a civil war -- but China still sees it as part of its territory.

The party's website came under attack in early April, redirecting visitors to a fake website, California-based FireEye said in a statement Thursday.

The tactic is one often used by Chinese hackers, it said.

Administrators fixed the problem the next day but the website was compromised again a few days later, suggesting the site is being monitored, according to the statement.

"FireEye believes this operation likely reflects continued efforts by China-based cyber espionage operators to collect intelligence related to the DPP as it moves Taiwan away from pro-mainland China policies," it said.

The government has raised concerns that its websites frequently fall prey to Chinese hackers.

Taiwan's Ministry of Transportation and Communication said in a report to a legislative committee last month that the scale of cyber attacks on Taiwan is "near warfare."

It added the most active hackers are from the mainland and had infiltrated the island's systems including defence, air traffic, and communication.

The defence ministry says it will establish a "cyber army", one of the policies put forward by Tsai during her presidential campaign.

A "Fourth Service" should be formed along with army, navy, and air force to protect "national digital territory," according to the DPP's proposal.

However, the DPP played down the findings of the new FireEye report and said it was not currently seeing "unusual hacking activities".

"The DPP has always put great importance on cyber safety," spokesman Wang Min-sheng told AFP.

Wang added that the party is not in contact with FireEye and that the security firm had been monitoring its website independently.