Stock futures crept higher on Tuesday in cautious trading as uncertainty reigned after separate terror attacks in Berlin, Zurich and Turkey on Monday. 

S&P 500 futures were up 0.2%, Dow Jones Industrial Average futures added 0.13%, and Nasdaq futures rose 0.14%. 

News broke late Monday afternoon that a truck had plowed through the crowd at an outdoor Christmas market in Berlin. Twelve are reportedly dead and 48 have been injured, some severely. Police said the event was "probably a terror attack." The attack echoes a similar act of terror in Nice, France, on Bastille Day earlier this year in which a cargo truck plowed into a crowd, killing 86 and injuring more than 400.

Separately, a gunman shot up a mosque in Zurich on Monday, injuring three. Swiss police have reportedly discovered a body in the vicinity believed to be the shooter. The mosque was popular among Somali migrants. 

The Russian ambassador to Turkey was shot and killed in Ankara, Turkey, on Monday. Russia has called the assassination an act of terrorism. The two countries have had tenuous relations as the civil war in Syria spilled over into bordering Turkey. Russia backs Syrian President Bashar al-Assad against rebel troops in Syria.

The three separate acts of terror escalated worries over terrorism worldwide, a concern President-elect Donald Trump often flamed during his campaign. 

Safe-haven assets, including currencies, were on the move after the series of terror attacks. The Dollar Index, in particular, was on a tear, climbing 0.44% to trade at 103.58. The index was on track to close at its best level in roughly 14 years. 

The Dow looked to continue its march toward the psychologically important 20,000 on Tuesday, a level it flirted with last week. The Dow has moved within 50 points of the target, but hasn't yet clinched it. Markets have moved higher in response to optimism over Trump's proposed spending plans. Trump's administration, viewed as Wall Street friendly, has already backed deregulation, infrastructure spending and tax cuts.

It's an empty day for economic data, though the calendar should heat up in the back half of the week. There will be a number of data points for investors to trade on including existing home sales on Wednesday, the third and final estimate of third-quarter gross domestic product, and durable goods orders on Thursday, and new home sales data on Friday. This is the final full week of trading of the year.

Rite Aid (RAD - Get Report) jumped 6% in premarket trading after agreeing to sell 865 of its stores to Fred's  (FRED - Get Report) for $950 million. The move is part of Rite Aid and Walgreens Boots Alliance (WBA - Get Report) plans to sell off assets in order to gain approval from the Federal Trade Commission for its merger. 

Walgreens is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells WBA? Learn more now.

General Mills (GIS - Get Report) reported second-quarter adjusted earnings of 85 cents a share, missing Wall Street estimates by a penny. Net sales in the quarter fell 7% to $4.1 billion because of lower organic net sales and the divestiture of the North American Green Giant business, the company said.

BlackBerry (BBRY) climbed nearly 2% after posting surprise profit, a sign its turnaround plans have begun to gain traction. The company earned an adjusted 2 cents a share, higher than consensus of breakeven earnings. Revenue of $289 million fell short of estimates of $330 million. 

Darden Restaurants (DRI - Get Report) reported a surge in second-quarter profit. Earnings nearly doubled to 64 cents a share over the quarter, coming in as analysts' expected. Revenue of $1.64 billion came in slightly short of estimates, while same-store sales rose 1.7%, 200 basis points above forecasts. Same-store sales at Olive Garden rose 2.1%.