Wall Street stocks opened slightly lower Monday on lingering worries about a potential Greek default as investors anticipated Apple's launch of a ramped-up music service.

Five minutes into trade, the Dow Jones Industrial Average was at 17,840.82, down 8.64 points (0.05 percent)

The broad-based S&P 500 slipped 0.82 (0.04 percent) to 2,092.01, while the tech-rich Nasdaq Composite Index lost 0.91 (0.02 percent) to 5,067.55.

German Chancellor Angela Merkel warned Greece that it did not have much time left to secure a deal to unlock billions in rescue funds. Greece needs creditors to release money in order to meet IMF debt payments totalling 1.6 billion euros ($1.8 billion) by the end of June.

At its annual developer conference in California, Apple was expected to unveil a subscription music streaming service for $10 monthly. Shares of the tech giant were flat.