"Stocks are still the only game in the town," Jim Kee, president and chief economist of San Antonio-based South Texas Money Management, told Bloomberg News. "Pullbacks possibly, but ultimately stocks will keep grinding higher."
The S&P 500 last traded at 1,963.54.
"We still think a move into the 1,980-2,000 level is possible, but it will not be a huge surprise if 1,950 is revisited multiple times as we move through the summer months," Todd Salamone, senior vice president of research at Schaeffer's Investment Research in Cincinnati, Ohio, told Reuters.
Meanwhile, San Francisco Federal Reserve President John Williams said the central bank won't raise its benchmark interest rate "for some time". Last week St Louis Fed President James Bullard rattled markets saying the US economy was performing much better than most realised, predicting the Fed would lift its key by the end of in the first quarter of 2015.
"I am aware that not everyone is a fan of the Fed or of accommodative policy," Williams said in a speech in Sun Valley, Idaho, on Monday. "But the bottom line is, it has worked. And the asterisk is that it's not permanent. We won't raise interest rates for some time, which is the real marker of tightening policy."
He later told reporters that a rate hike would not be appropriate until the second half of 2015, Reuters reported.
"I see real GDP growth averaging a bit above 3 per cent in 2015 and 2016, which should be enough to generate relatively strong job growth," Williams said. "I expect the unemployment rate to gradually decline, hitting about 6 per cent at the end of this year, falling below 5.5 per cent by the end of next year, and reaching my estimate of the natural rate by the first half of 2016."
In Europe, the Stoxx 600 Index edged lower to finish the session at 341.86. The UK's FTSE 100 fell 0.2 per cent, while France's CAC 40 declined 0.3 per cent. Germany's DAX added 0.2 per cent.
A report showed German retail sales posted a surprise drop of 0.6 per cent in May.
A deal between US authorities and French bank BNP Paribas is expected to be announced within days. Reports suggest the bank will have to pay as much as US$9 billion in penalties and lose the ability to do some business in the US.