By Johann M Cherian and Purvi Agarwal

(Reuters) -U.S. stock index futures inched higher on Tuesday, building onto gains, while investors assessed the implications Donald Trump's tariffs on top trade partners could have on the local economy.

The president-elect said he would impose a 25% conditional tariff on Canadian and Mexican imports that could violate a free-trade deal he negotiated during his previous term. He also outlined "an additional 10% tariff, above any additional tariffs" on imports from China.

At 6:53 a.m. ET, Dow E-minis were up 80 points, or 0.18%, S&P 500 E-minis were up 13.75 points, or 0.23% and Nasdaq 100 E-minis were up 57.25 points, or 0.27%.

Automakers such as Ford and General Motors -that have highly integrated supply chains across Mexico, the U.S. and Canada - lost 2.5% and 3.3%, respectively in premarket trading.

"New tariffs from the U.S. could intensify the global trade frictions and may impact the economic growth prospects in the longer term," strategists at ING bank said.

However, some analysts say that the threats might not materialise into policies.

"There has been a view among some investors that Trump's tariff talk was a negotiating tactic, a threat rather than a promise. That might still end up the case...," said Dan Coatsworth, investment analyst at AJ Bell.

Yields on Treasury bonds that had slipped in the previous session following Scott Bessent's selection as incoming Treasury secretary, rose and pressured riskier equities.

The benchmark S&P 500 touched a record high on Monday and logged its sixth-straight session of gains and a drop in yields lifted rate-sensitive sectors such as real estate and regional banks.

Investors also rotated into small-cap companies, that helped the Russell 2000 index scale an all-time high on Monday, surpassing the previous record hit three years ago. On Tuesday, futures tracking the Russell dropped 0.3%.

On the data front, a consumer confidence survey is due at 10:00 a.m. ET and post-noon markets will assess minutes from the central bank's meet earlier this month. However, top on the radar this week is the personal consumption expenditure report due on Wednesday.

Minneapolis Federal Reserve President Neel Kashkari, typically on the hawkish end of the U.S. central bank's policy spectrum, said he is open to cutting interest rates again next month.

Analysts say Trump's trade and fiscal policies, though seen as a positive for companies and economic growth, could stoke inflation pressures and slowdown the Fed's monetary policy easing cycle.