At midday AEDT on Wednesday, the benchmark S&P/ASX200 index was down 35.7 points, or 0.43 per cent, to 8,338.2, while the broader All Ordinaries had dropped 39 points, or 0.45 per cent, to 8,590.2.
In Russia, officials said they had shot down five of the six long-range weapons Ukraine had fired into its territory, but explosions were heard at a ammunition supply depot in Karachev.
Hours later, Russian President Vladimir Putin formally lowered the threshold for Russia's use of nuclear weapons, a move quickly condemned by the US as "bellicose and irresponsible."
At midday nine of the ASX's 11 sectors were lower, with materials/mining and utilities slightly higher.
Tech was the biggest loser with a 1.0 per cent dip, after being the biggest gainer on Tuesday.
Xero had fallen 1.6 per cent, Technology One was down 2.7 per cent and Appen had retreated 10.4 per cent.
The big four banks were mixed, with CBA up 0.4 per cent, Westpac down 0.4 per cent, NAB dipping 0.3 per cent and ANZ flat.
In the heavyweight mining sector, BHP was basically flat, while Fortescue had gained 1.4 per cent, Rio Tinto had added 0.3 per cent and Northern Star had advanced 1.5 per cent.
In the consumer discretionary sector, PWR Holdings had plunged 30.5 per cent to a three-year low of $6.31 after the high-tech cooling parts supplier for the performance automotive industry said it expected to earn as little as $3.2 million in profit this half-year, down from $9.8 million a year ago.
Managing director Kees Weel reiterated this was a transition year for the Queensland company as it moved to a new headquarters in Stapylton.
Nick Scali was down 0.5 per cent after the furniture retailer said one of its freight forwarders and customs agents had entered liquidation, leading to a significant number of its containers being delayed at ports.
In currency, the Australian dollar was at an eight-day high against its US counterpart, buying 65.33 US cents, from 65.08 US cents at Tuesday's ASX close.
