* Apple down after Needham downgrade
* Energy stocks flat despite oil jump
* Defense stocks rise premarket
* Futures down: Dow 0.63%, S&P 0.56%, Nasdaq 0.69% (For a live blog on the U.S. stock market, click or type LIVE/ in a news window.)
By Sruthi Shankar
Jan 6 (Reuters) - U.S. stocks were set fall for a second straight session on Monday as escalating tensions between the United States and Iran prompted investors to seek refuge in safer assets such as gold and government bonds.
After ending 2019 on a strong note, Wall Street's main indexes have been knocked off record levels after the killing of a top Iranian general by the United States last week raised the threat of a new Middle East conflagration.
Tehran has threatened to avenge the killing of its commander, Qassem Soleimani, while President Donald Trump has warned that the United States would strike back, "perhaps in a disproportionate manner", if Iran retaliated.
"Tensions in Middle East raise concerns for investors following what has been a really great period in markets," said Rick Meckler, partner at Cherry Lane Investments in New Vernon, New Jersey. "Certainly, some are using this as a reason to step back a little bit."
Brent crude futures topped $70 per barrel after Trump also threatened to impose sanctions on Iraq if U.S. troops were forced to withdraw from the country.
Oil majors Chevron and Exxon Mobil were flat after trading marginally higher in early hours.
Shares of Lockheed Martin, the world's largest defense contractor, rose 1.7%, while peers Northrop Grumman and Raytheon gained about 1.5%.
At 08:59 a.m. ET, Dow e-minis were down 179 points, or 0.63%. S&P 500 e-minis were down 18 points, or 0.56% and Nasdaq 100 e-minis were down 60.5 points, or 0.69%.
The latest geopolitical concerns have added to fears of anemic earnings growth and a less supportive Federal Reserve derailing the longest bull run in U.S. equities.
"Until we get to the next earnings season, absent any big news, investors are probably reluctant to commit a lot of new capital at these levels, but are also not interested in pulling back, which leaves markets a bit range-bound," said Meckler.
Apple Inc shares fell about 1% after brokerage Needham cut its rating to "buy" from "strong buy", saying the stock outperformed significantly in 2019.
Shares of Boeing Co dropped 1.2%. A Wall Street Journal report said the planemaker was considering plans to raise more debt to bolster its finances after the grounding of its 737 MAX jet.
New York-listed shares of Nio Inc jumped 10.7% after the Chinese electric carmaker reported higher deliveries in December, compared with the previous month.
Reporting by Sruthi Shankar in Bengaluru; Editing by Sriraj Kalluvila