* Citigroup one of S&P's biggest gainers after results
* U.S. March retail sales post biggest gain in 1-1/2 years
* Brent crude prices jump; energy stocks follow
* Dow up 0.7 pct; S&P 500 up 0.6 pct; Nasdaq up 0.5 pct (Updates to afternoon trading, changes byline)
By Ryan Vlastelica
NEW YORK, April 14 (Reuters) - U.S. stocks rose on Monday, rebounding after a sharp selloff in the previous session as strong results from Citigroup and bullish retail sales data lifted sentiment.
While concerns over the possible escalation of hostilities in Ukraine added an element of caution to the market, gains were broad and all 10 major S&P 500 sectors rose on the day.
Citigroup led financial shares higher after the bank reported quarterly earnings that beat expectations, aided by a smaller loss on its troubled assets even as its revenue declined. The stock rose 4.6 percent to $47.78 while both the S&P financial index and the KBW Banks index gained 0.7 percent.
Among other financials, Bank of America Corp shares rose 1.5 percent to $16 while Morgan Stanley was up 1.8 percent at $28.99.
"People took heart from these results being better than expected, driving other banks up in sympathy," said John Carey, portfolio manager at Pioneer Investment Management in Boston. "People seem refreshed and interested in stocks again after the recent weakness we've had, so there seems to be some bargain hunting as well."
Equities were also boosted by data showing U.S. retail sales recorded their largest increase in 1-1/2 years in March, a bigger gain than had been anticipated and the latest sign the economy was emerging from its weather-induced slumber.
"This is encouraging, especially after some softness earlier this year and worries about weather," said Carey, who helps oversee about $220 billion in assets. "Consumers seem to have come back, which is a hopeful sign for the rest of the year."
The Dow Jones industrial average was up 112.83 points, or 0.70 percent, at 16,139.58. The Standard & Poor's 500 Index was up 11.63 points, or 0.64 percent, at 1,827.32. The Nasdaq Composite Index was up 19.53 points, or 0.49 percent, at 4,019.27.
Pro-Russian separatists ignored an ultimatum to leave occupied government buildings in eastern Ukraine as a threatened military offensive by government forces failed to materialize. Rebels in the town of Slaviansk issued a bold call for Russian President Vladimir Putin to help them.
Tension between Moscow and the United States increased over the weekend as a Russian fighter aircraft made repeated low-altitude close-range passes near a U.S. ship in the Black Sea.
Russian stocks fell 1.3 percent and the rouble hit its weakest in three weeks against the U.S. dollar as Ukraine's preparedness to fight heightened fears of Russian military intervention and more Western sanctions against Moscow.
Brent crude prices climbed on concerns about supply disruptions or sanctions against Russia. The S&P energy index rose 1.4 percent and was one of the best-performing sectors on the day.
Military intervention from Russia "would give the market reason for a further correction," said Jack de Gan, chief investment officer of Harbor Advisory Corp in Portsmouth, New Hampshire, adding that the market should be more concerned about that prospect.
On Friday, JPMorgan's disappointing earnings were partly to blame for the day's selloff. Biotech and other momentum stocks led the Nasdaq Composite lower, pushing the index below 4,000 for the first time in two months. The Nasdaq biotech index on Friday closed 21 percent below its record closing high hit Feb. 25, entering bear market territory.
While the index rebounded in early trading on Monday, it subsequently pared those gains to turn flat, taking the Nasdaq down from session highs.
Medtronic shares fell 2 percent to $58.02 after a U.S. court ruling temporarily stopped sales of the company's aortic heart valve replacement system in the United States because of a patent infringement. Shares of Edwards Lifesciences , which was on the other side of the ruling, rallied 12 percent to $81.62 as the S&P's biggest gainer.
Shares of Aspen Insurance Holdings jumped 10.6 percent to $43.54 after Endurance Specialty offered to buy Aspen for $3.2 billion in cash and stock. Endurance shares fell 1.4 percent to $53.09. (Reporting by Rodrigo Campos; Editing by Chizu Nomiyama, Meredith Mazzilli and Jan Paschal)