The Standard & Poor's 500 Index fell to a two-month low amid declines in airline and semiconductor shares, as investors considered the timing of an interest-rate increase and the outlook for Greece's debt talks.

Reports on consumer sentiment and retail sales are due this week, both of which are forecast to show an improving economy. Jobs data Friday showed the strongest hiring in five months and the biggest wage gains in two years, bolstering bets the Federal Reserve will raise interest rates this year.

Investors are also looking for signs of progress in negotiations between Greece and its international creditors. With talks to resume in Brussels on Monday, Prime Minister Alexis Tsipras faced a united front from Group of Seven leaders calling for movement to end the impasse and avert the risk of wider economic reverberations.

The S&P 500 posted back-to-back weekly declines for the first time since March as investors weigh equity valuations amid the potential Fed rate increase this year.

Consumer expectations for inflation rebounded in May, according to a Fed Bank of New York survey, as officials look for evidence that price pressures are firming.

In the quarter after the last 12 tightening cycles began, price-earnings ratios on the benchmark index contracted by an average of 7.2 percent. It's something else to worry about as the Fed prepares to lift rates in an economy that is still far from booming.

Should policy makers move before January, they would be doing so in a year when U.S. profits are forecast by analysts to increase 1.4 percent. That represents the weakest growth at the start of a tightening cycle since 1980.