KUALA LUMPUR, March 5 — Australian Prime Minister Tony Abbott conceded today that the search for missing Malaysia Airlines Flight MH370 cannot continue at current intensity perpetually, although he hoped it will continue.

Addressing his Parliament to mark a “harrowing 12 months of uncertainty and sorrow”, Abbott reassured the families of those on board MH370 that Canberra is still optimistic that the search will find the missing jetliner.

“My pledge is we are taking every reasonable step to bring your uncertainty to an end. I do reassure the families of our hope and expectation that the ongoing search will succeed,” Abbott said, as quoted by Sydney-based daily The Australian.

“I can’t promise that the search will go on at this intensity forever, but we will continue our very best efforts to resolve this mystery and provide some answers.”

Opposition Leader Bill Shorten also gave his support, telling the families of seven missing Australians that the country’s parliament was firmly behind them.

“We stand united in the support for our skilled work of the international search team and we’re united in our deep respect for the memory of the missing,” said Shorten.

The Boeing 777 vanished a year ago Sunday carrying 239 people en route from Kuala Lumpur to Beijing and is believed to have gone down in one of the deepest and most remote areas of the Indian Ocean far off the Western Australia coast.

Chief commissioner of the Australian Transport Safety Bureau Martin Dolan said on Tuesday that while several man-made items — mostly shipping containers — have been detected during a sonar search, they had found nothing resembling debris from the Malaysia Airlines jet.

Australian and Malaysian authorities have narrowed the search area to a vast 60,000 sq km zone — and they have so far scoured around 40 per cent of it, Dolan said.

Three of the four search vessels — Fugro Equator, Fugro Discovery and GO Phoenix — are using sophisticated sonar systems to scan the complex terrain that plunges to depths of 4,000m.

The Fugro Supporter, which joined the search earlier this year, has an autonomous underwater vehicle that moves over the ocean floor more slowly.

The search is jointly funded by Australia and Malaysia, with some AUD$120 million (RM325 million) pledged so far.