US stocks were losing ground at the open as the crisis in Ukraine ramped up a gear, with fears circulating of a potential Russian invasion into the country.
The country's president, who has cancelled a visit to Turkey, says troops have been moved across the border to support separatists.
Pro-Russian fighters have however taken a coastal town and threatened the port city of Mariupol.
Russia has come back and said no forces were crossing the border.
The benchmark Dow is down 94 points to 17,025, while the S&P500 lost nine points and Nasdaq shed 22 points to move to 1,991. The losses were the most in three weeks.
In London, Britain's leading share index is down 23 at the time of writing.
A look at US shares today would be perhaps incomplete without mentioning Alibaba, which has been piquing media interest all day, through its results release.
The firm, which is tipped to raise over US$20bn in its stock market debut in New York next month, unveiled big profits in its second quarter.
The mobile tech specialist controls most of China's rapidly expanding e-commerce market.
On a day where volumes were light as traders go off for summer holiday, among the losers was clothes retailer Abercrombie & Fitch Co as second-quarter sales fell more than Wall Street had expected.
Abercrombie has been working to turn round the business since last year.
Back in London and it was FTSE 250 constituent Cambridge chipmaker CSR (LON :CSR) that provided the takeover chatter today and its shares zoomed up 34%.
The company this morning responded to recent media talk by confirming that it has received an approach from Microchip Technology.
However, chips aren’t as cheap as they say and the price proposed by its US rival has been rejected by the board, which is considering its options.
Among smaller caps, market darling Gulf Keystone (LON:GKP), which operates in the threatened region of Kurdistan in Iraq, was out of favour today after hinting it may miss production targets due to the evolving situation in the region. Shares dropped 7.55%.
Tekcapital’s (LON:TEK) acquisition of inventions web site InventionEvaluator.com site is an ideal way to complement its own business of locating, screening and acquiring intellectual property (IP), according to broker Northland today. Shares in the company rose 4.09%.