UK's main indexes tracked a slump in global markets on Tuesday as tensions between Russia and Ukraine escalated, while a surge in oil prices on supply concerns lifted oil majors BP and Shell capping some of the losses on the commodity-heavy index.
The FTSE 100 fell 0.5% in morning trade, while the domestically focussed mid-cap index declined 0.6%.
The United States and its European allies are poised to announce new sanctions against Russia after President Vladimir Putin recognised two breakaway regions in eastern Ukraine and signed a decree for the deployment of troops to those areas.
Russia-exposed miners Polymetal International, Petropavlovsk and EVRAZ fell between 4.5% and 12.5% on the possibility of sanctions.
Oil majors BP and Shell rose 1.6% and 2.1%, respectively, as oil prices rallied on fears of supply disruption as Europe's eastern flank stood on the brink of war.
"The mood is totally risk off," said Ipek Ozkardeskaya, senior analyst at Swissquote.
"The losses are more limited in FTSE compared to its European peers because the index is commodity heavy and the tensions in Russia are pushing their prices higher right now."
The energy sub-index has gained 21.4% since the start of 2022 and has been the biggest boost to the benchmark FTSE 100 index.
Lender HSBC fell 1.3%, tracking a decline in its Hong-Kong listed shares in a weaker market, despite bringing forward its key profitability target by a year and more than doubling its annual profits.
Retail stockbroker Hargreaves Lansdown fell 18.6% after reporting a drop in half-year profit, hurt by lower interest rates and easing market volatility.
Medical products maker Smith+Nephew rose 2.2% on naming Siemens Healthineers' Deepak Nath as its new chief executive, while Holiday Inn-owner IHG gained 1.9% as its annual profit beat estimates.