The Dow Jones Industrial Average rose 16.05 points, or 0.10 percent, to 16,569.98. The S&P 500 added 5.33 points, or 0. 28 percent, to 1,936.92. The Nasdaq Composite Index climbed 30.43 points, or 0.70 percent, to 4,401.33.
With no major economic data due Monday, investors were closely monitoring the latest geopolitical developments that the Ukraine crisis seemed subsiding, and Israel and Hamas agreed Sunday to launch a new 72-hour truce.
Russia is sending a humanitarian convoy to Ukraine in collaboration with representatives of the International Committee of the Red Cross, President Vladimir Putin said Monday in a phone conversation with European Commission President Jose Manuel Barroso.
Responding to these positive signs, the U.S. stock market extended gains into a second consecutive session, after the Dow and the S&P 500 on Friday posted their biggest percentage gains since early March on reports that Russia ended its military drill near the Ukrainian border.
However, the market pared earlier gains in the afternoon session, as geopolitical risks kept investors from making a big move before they are clear about the situation in Ukraine and Gaza.
The second-quarter earnings season is winding down, with just 16 S&P 500 companies expected to report quarterly results this week, including big retailers such as Wal-Mart and Macy's.
Analysts said that corporate earnings in the second quarter turned out to be generally upbeat, which is a major factor that sent the U.S. equity market to uncharted territory before the recent correction.
According to latest data from Thomson Reuters, 90 percent of the S&P 500 companies have reported second-quarter results, among which 67.4 percent have reported earnings above analysts' expectations and 62.4 percent have published revenue above market forecast.
Thomson Reuters estimated that the blended earnings-per-share growth of S&P 500 companies will be 8.3 percent, while revenue growth at 4.4 percent.
The CBOE Volatility Index, widely considered as Wall Street's fear gauge, sank 9.77 percent to end at 14.23 on Monday.
In other markets, the U.S. dollar strengthened against most major currencies on eased geopolitical tensions in Ukraine and Iraq.
In late New York trading, the euro fell to 1.3383 dollars from 1.3410 dollars of the previous session. The greenback bought 102. 18 Japanese yen, higher than 102.04 yen of the previous session.
U.S. crude price rose. Light, sweet crude for September delivery edged up 43 cents to settle at 98.08 dollars a barrel on the New York Mercantile Exchange.
Gold futures on the COMEX division of the New York Mercantile Exchange fell slightly as U.S. equities strengthened. The most active gold contract for December delivery lost 0.5 dollar, or 0. 04 percent, to settle at 1,310.5 dollars per ounce.