(CBS) — Stocks closed sharply lower on Thursday as the lack of progress in Greek debt negotiations and the recent selloff in bonds kept traders on edge before Friday’s key jobs report.

“I think Greece in the primary driver of today’s selling pressure, maybe also a delayed reaction to yesterday’s run up in bond yields,” Jim Welsh, Portfolio Manager at ForwardInvesting.com, tells Andy Giersher.

He also noted the S & P 500 has recently tested some key technical levels.

The NASDAQ lost 40, the S&P 500 was down 18 and the Dow Jones industrial average shed 170 points, settling below the 18,000 mark. The Dow and S&P 500 both closed below their 50-day moving average.

“The market could continue to head higher, until a reason to sell shows up and really challenges people’s constructive outlook about what they expect over the next six to twelve months,” Welsh said.