Sunday's deal with Iran was the first significant progress in years to curtail that country's nuclear ambitions. It could reduce the risk of conflict, improve trade and boost global oil supplies by making it easier for Iran to sell its crude onto the global market.
In other news, shares of Wal-Mart rose 57 cents, or 0.7 percent, to $80.38 after the company announced its CEO was stepping down. Alcoa climbed 44 cents, or 5 percent, to $9.68 after Goldman Sachs upgraded the company to "buy'' from "neutral,'' citing potential growth in its aluminum products business.
Stocks overall have soared this year as a combination of solid corporate earnings, a strengthening economy and easy-money policies from the Federal Reserve draw investors to stocks. Stocks have also gained because they offer an attractive alternative to bonds, where interest rates remain close to all-time lows.
The Dow Jones industrial average rose 29 points, or 0.2 percent, to 16,094 in early afternoon trading Monday. The Standard & Poor's 500 index rose one point, or 0.1 percent, to 1,806, extending its upward climb after closing above 1,800 for the first time Friday.
The S&P 500 has risen seven straight weeks and is up 27 percent in 2013, its best performance in 15 years.
The market edged past more round-number milestones Monday. The Nasdaq composite was up five points, or 0.1 percent, to 3,996 after it earlier breached the 4,000 mark, a level it hasn't seen since Sept. 7, 2000, during the dot-com bubble.
However, an increasing number of investors believe that stocks have run their course for 2013 and stocks are due for a pullback soon.
"I would like to see this market take a breather,'' said Jim Lauder, a fund manager for Wells Fargo Advantage Dow Jones Target Date Funds.
The energy sector was the biggest decliner among the 10 S&P 500 industry groups Monday, due to the lower oil prices. The price of benchmark U.S. crude was down 90 cents, or 1 percent, to $93.96 a barrel. Energy companies Halliburton, Transocean and Anadarko Petroleum all fell sharply.
Trading is expected to be light this week. Stock and bond markets are closed Thursday in observance of the Thanksgiving holiday. On Friday, the New York Stock Exchange and Nasdaq will close early.
Investors will focus on Black Friday, when the holiday shopping season officially starts. Due to the lateness of Thanksgiving, the Christmas shopping season is a week shorter than usual, and that could affect the amount of shopping people can do. An increasing number of retailers are opening up on Thanksgiving to draw in customers.