Feb 28 (Reuters) - Australian shares edged lower on Monday after Western nations imposed new sanctions on Russia for its invasion of Ukraine, while energy stocks rose as oil prices jumped on supply disruption fears.

The S&P/ASX 200 index was down 0.1% at 6,991.0 by 0023 GMT, reversing course after rising 0.3% in early trade. The benchmark rose 0.1% on Friday but lost 3.1% last week.

President Vladimir Putin put Russia's nuclear deterrent on high alert on Sunday in the face of a barrage of Western reprisals for his war on Ukraine, which said it had repelled Russian ground forces attacking its biggest cities.

In Australia, financials fell 0.7% and led the decline. National Australia Bank lost 0.6%, while the other three "Big Four" banks gained between 0.1% and 0.3%.

Healthcare stocks lost 1% with CSL Ltd down 1.5%, while tech stocks fell 1.3%.

Among gainers, energy stocks rose 1.3% after oil prices jumped more than $7 in early trade on fears of supply disruption.

Sector majors Santos and Woodside Petroleum advanced 2.1% and 2.3%, respectively.

Miners followed suit to gain 1.2%. BHP Group climbed 1.9%, while Rio Tinto rose 1.4%.

In corporate news, buy-now-pay-later firm Zip Co Ltd said it would buy U.S.-based Sezzle Inc in a A$491 million ($352.59 million) deal, as it looks to further expand its reach in the United States and take on rivals such as Afterpay.

Zip and Australia-listed shares of Sezzle were halted for trading.

New Zealand's benchmark S&P/NZX 50 index was up 0.1% at 11,938.22.

The Reserve Bank of New Zealand's chief economist said the country's trade links with Russia and Ukraine were minor but there could be some impact through market volatility and commodity prices. (Reporting by Himanshi Akhand in Bengaluru; Editing by Subhranshu Sahu)