SYDNEY-- Leighton Holdings Ltd.'s first-half net profit fell 20%, though the company signaled progress in weathering a global-mining slowdown by sharpening focus on major construction contracts, including airports and Asian casinos.

Australia's biggest construction company cited restructuring costs and the absence of one-off gains from the sale of telecoms assets that had boosted earnings a year earlier for its drop in profit for the six months through June. On other measures, Leighton said business was improving, with net margins strengthening and net debt declining.

Sydney-based Leighton has been working to rebuild its balance sheet and bolster its flagging share price after problematic infrastructure projects in Australia led the company to report its first annual loss in decades in 2011. Its order book increasingly has been filled by deals to build projects from casinos in Macau to airports in the Middle East, as contracts to move earth at mine sites such as Australia's vast coal pits moderate.

On Monday, the company reported an underlying net profit--stripping out one-time charges--of 319 million Australian dollars (US$299.7 million) for the six months through June, up 25% from the corresponding period a year earlier. Leighton said its net margin lifted to 2.7% from 2.2% in the year earlier period and just 1% in the first half of 2012.

Management reiterated expectations the group would record an underlying profit of A$540 million to A$620 million this calendar year, underpinned by a strengthening pipeline of construction work in Asia and oil-and-gas projects in Australia.

Underscoring Leighton's confidence in its outlook, the company lifted its interim dividend 27% to 57 cents a share.

Leighton said a lift in revenue from construction work during the half offset a decline in turnover from its mining business, which has suffered as Australia's mining companies have closed pits, delayed projects and laid off workers to protect profits from falling commodity prices and a strong Australian dollar. Construction revenue rose 5% on year to A$7.7 billion, while contract mining revenue fell 11% to A$2.1 billion.

Australian-based Leighton is controlled by Germany's Hochtief AG, which has been run for the past four years by Spain's Actividades de Construccion y Servicios SA, or Grupo ACS. Earlier this year, Hochtief increased its controlling stake in the company to 70% and ousted Leighton's top management, including its chairman and chief executive.

Marcelino Fernandez Verdes, Leighton's new chief executive, said he was focused on strengthening the company's balance sheet amid a continuing strategic review aimed at cutting debt, trimming working capital and further bolstering profit margins. Leighton's shares have roughly halved in value since early 2008, giving it a current market value of A$7.51 billion.

Leighton last month announced it may sell assets--including John Holland, a business that generates a fifth of its revenue--in a drive to halve the group's gearing, or debt-to-equity level, to 20% by the end of the year. Mr. Fernandez Verdes didn't provide an update on plans to unload some parts of the group, except to say negotiations with possible investors were in progress.

"We expect to further increase net margins as we simplify the structure of the group," he said.

With the primary focus on repairing its balance sheet, the company also has been chasing money it is owed for construction work, particularly at its Habtoor Leighton Group joint venture in the Middle East, which has previously faced substantial write-downs.

The company said receivables rose to A$5.5 billion at June 30, compared with A$5.0 billion six months earlier, although attributed this in part to lengthy payment cycles on major liquefied natural gas projects in Australia. Analysts previously have raised concerns that a rise in overdue payments would hamper the company's cash flow when management has been looking to bolster payouts and cut debt.

Write to Rhiannon Hoyle at rhiannon.hoyle@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires