U.S. stocks closed sharply lower Monday, with the Dow Jones Industrial Average turning negative for the year. Monday's declines were led by losses in the technology sector.

The Dow (INDEXDJX:.DJI) fell 82.91 points, or 0.46 percent, to close at 17,766.55. The Standard & Poor’s 500 index (INDEXNASDAQ:.IXIC) fell 13.55 points, or 0.65 percent, to end at 2,079.28. The Nasdaq composite (INDEXSP:.INX) lost 46.83 points, or 0.92 percent, to finish at 5,021.63.

For the year, the Dow has lost 55 points, or 0.31 percent. However, the S&P 500 index has added 21 points, or 1 percent, while the Nasdaq has gained 286 points, or 6 percent.

Chipmaker Intel Corporation (NASDAQ:INTC) led the Dow lower, dropping nearly 2 percent. Meanwhile, Exxon Mobil Corporation (NYSE:XOM) was the largest gainer in the blue-chip index, up nearly 1 percent.

Shares of Dow component Apple Inc. (NASDAQ:AAPL) fell 0.5 percent after the tech giant kicked off its five-day annual Worldwide Developers Conference. CEO Tim Cook announced the company would launch its Apple Music service June 30 for $9.99 a month, and also unveiled new versions of the iOS and OS X software.

FBR Capital Markets maintained its Outperform rating on Apple following the first day of the event. "While there were no major surprises at today's keynote, we would characterize the event so far with a major focus on software/services and, thus, helping lay the groundwork for Apple's next leg of growth on the software frontier, Watch and Apple Pay product categories," Daniel Ives, analyst at FBR Capital Markets, said in a research note Monday. 

Shares of Apple, which have gained around 40 in that last 12 months, dipped 0.5 percent Monday to close at $128.01.

The Dow Jones Transportation Average, which has already lost nearly 9 percent this year, dropped 2 percent Monday, led by a 7 percent decline from JetBlue Airways Corporation (NASDAQ:JBLU).

The Turkish stock market dropped more than 5 percent Monday while the Turkish lira dropped to a record low of 2.75 against the U.S. dollar after the ruling Justice and Development Party failed to win a majority in parliamentary elections for the first time in more than a decade.

The financial markets are nervous heading into the summer, says Jeff Kravetz, regional investment director at U.S. Bank Wealth Management. But it’s international geopolitical tensions that are making investors nervous, not the U.S.

Last week, Greece opted to delay a debt repayment to European creditors, sparking fears Athens is edging closer to bankruptcy. Greece bundled four installments due in June into a single 1.6 billion euro ($1.8 billion) lump sum now due on June 30 to the International Monetary Fund.

A poll last Wednesday and Thursday showed eight in 10 Greeks surveyed said they wanted to stay in the eurozone, according to Metron Analysis for the newspaper Parapolitika. The same poll showed 47 percent wanted the government to accept the proposal the creditors made last Monday, while 35 percent wanted to reject it.

Greek citizens favor staying in the eurozone even if that means tougher austerity measures. “We still believe cooler heads are going to prevail,” Kravetz said. “The Greek people realize it’s in their best interest to remain in the eurozone.”