* Yellen points to improving U.S. labor market
* Shooting death of Russian ambassador to Turkey briefly weighs
* Dow remains less than 1 percent away from 20,000
* United Tech rises after Credit Suisse upgrade; boosts Dow
* Indexes up: Dow 0.26 pct, S&P 0.25 pct, Nasdaq 0.47 pct (Updates to late-afternoon trading)
By Noel Randewich
Dec 19 (Reuters) - U.S. stocks rose on Monday with the Nasdaq Composite in record territory as investors snapped up technology heavyweights Microsoft, Apple and Amazon.com.
Major stock indexes trimmed gains after the Russian ambassador to Turkey was shot dead in Ankara.
The S&P technology index rose 0.66 percent, with Microsoft, Apple and Amazon.com lifting the Nasdaq Composite to within a hair of last Tuesday's record high close.
U.S. stocks have been on a tear since the Nov. 8 presidential election, with the S&P rising nearly 6 percent on bets that President-elect Donald Trump's expected deregulation and infrastructure spending will boost the economy.
"The Trump rally is still with us. Every time something's down for two days, people jump on it. People are looking for buying opportunities," said Jake Dollarhide, chief executive officer of Longbow Asset Management in Tulsa, Oklahoma.
The Dow Jones industrial average is less than 1 percent away from 20,000, a level it has never breached.
However, some investors warn that uncertainty around Trump's policies and the likelihood of them being approved by Congress pose major risks to current stock prices.
In a speech, Federal Reserve Chair Janet Yellen said the U.S. labor market has improved to its strongest in nearly a decade, suggesting wage growth is picking up and underscoring expectations the central bank will continue to raise interest rates next year.
At 2:43 pm ET, the Dow Jones industrial average was up 0.26 percent at 19,894.76 points and the S&P 500 had gained 0.25 percent to 2,263.8.
The Nasdaq Composite added 0.47 percent to 5,462.79.
Microsoft rose 2.25 percent, Amazon.com gained 1.11 percent and Apple climbed 0.77 percent. All three provided the biggest boost to the Nasdaq and the S&P 500.
United Technologies rose 1.8 percent, helping lift the Dow, after Credit Suisse upgraded the stock to "outperform" and increased its price target.
Walt Disney rose 1.4 percent after its "Rogue One: A Star Wars Story" movie scored the second-largest December opening in history.
Advancing issues outnumbered declining ones on the NYSE by a 1.81-to-1 ratio; on Nasdaq, a 1.52-to-1 ratio favored advancers.
The S&P 500 posted 12 new 52-week highs and no new lows; the Nasdaq Composite recorded 135 new highs and 29 new lows. (Additional reporting by Tanya Agrawal in Bengaluru and Rodrigo Campos in New York; Editing by James Dalgleish)