SYDNEY (AFP) -- Australian Prime Minister John Howard said Friday he was horrified by the latest Istanbul bomb attacks and lashed out at "perverse" anti-US protestors in London for not demonstrating against terrorism.

As Australia warned its citizens to avoid Turkey, Howard said he was stunned by the images of devastation from the two huge bomb attacks that killed at least 27 people and injured 450 in Istanbul.

"It's another example of the murderous, indiscriminate character of terrorism," he told commercial radio.

Howard said he was struck by the events in Turkey and the massive protest by more than 100,000 people in London against a state visit to Britain by U.S. President George W. Bush. "It struck me as rather perverse," he said. "They have a right to do so, but I have a right to question why they don't pour their bile and energy of demonstration into an attack on those people who are responsible for perpetrating these things."

Australia's foreign affairs department upgraded its travel advice, telling citizens to avoid non-essential travel to the country until further notice.

"Australians in Turkey should exercise extreme caution, particularly in commercial and public areas, and keep themselves informed of developments that might affect their safety," the government travel advisory warned.

Foreign Minister Alexander Downer said the travel advisory had already been upgraded after the bombing of two synagogues last week killed 25 people.

Turkey is a popular tourist spot with Australians, particularly young backpackers making the pilgrimage to the World War I battlefields of Gallipoli.

Australia's ambassador to Turkey Jonathan Philp said no Australians were believed to have been hurt in the attacks, which targeted the British consulate and the Istanbul offices of the British bank HSBC.

Philp described British Consul-General Roger Short, who was killed in the attacks, as "a friend of Australia".