Australian shares retreated on Monday amid reports that the process to reach a peace agreement between Iran and the US had stalled over the weekend.

The S&P/ASX 200 Index fell 0.49%, or 42.60 points, to close at 8,701.80.

Brent crude oil futures rose over 4% to trade around $105 per barrel after the US rejected Iran's response to a US proposal to end the conflict and reopen shipping through the Strait of Hormuz.

On the domestic front, the total number of dwellings approved in Australia fell around 11% to 17,300 in March, seasonally adjusted, from 19,339 in the previous month, according to final figures released by the Australian Bureau of Statistics.

In company news, CSL (ASX:CSL) lowered its guidance for fiscal 2026 and expects to recognize about $5 billion of additional non-cash, pre-tax impairments across fiscal 2026 and 2027 beyond those the company disclosed earlier this year.

The biotechnology company now expects fiscal 2026 revenue of around $15.2 billion and net profit after tax adjusted to exclude amortization of around $3.1 billion, both on a constant-currency basis. Its shares closed down 15%, earlier hitting their lowest since December 2016.

Dyno Nobel (ASX:DNL) reported fiscal first-half earnings of AU$0.089 per share, excluding individually material items, up from AU$0.046 a year earlier. Revenue from ordinary activities for the six months ended March 31 was AU$1.9 billion, compared with AU$2.25 billion a year earlier. It shares rose 7% on close after earlier hitting their highest since January 2023.

Lastly, Inghams Group (ASX:ING) reaffirmed its fiscal 2026 guidance for underlying earnings before interest, taxes, depreciation, and amortization of AU$180 million to AU$200 million. Its shares jumped 7% on market close.