Adding details, analyst comment from paragraph 3

SEOUL, Jan 27 (Reuters) - Hyundai Motor 005380.KS shares fell as much as 4.8% in morning trade on Tuesday, after U.S. President Donald Trump said in a social media post that he will raise tariffs on South Korean goods including autos from 15% to 25%.

Shares in sister automaker Kia Corp 000270.KS and affiliate Hyundai Mobis 012330.KS also fell as much as 6% and 5.7%, respectively, compared with a 1.2% drop in the benchmark KOSPI .KS11.

Trump said on Monday he was increasing tariffs on South Korean imports into the United States related to autos, lumber and pharmaceuticals to 25%, as he accused the ally's legislature of "not living up" to its trade deal with Washington.

It was not immediately clear when the tariff hike would take effect, or what specifically triggered Trump's directive.

Some analysts said, however, that South Korea-U.S. trade negotiations had already been agreed upon at the presidential level and ultimately it should be a matter of time before any issues are resolved.

Senior analyst Kim Joon-sung at Meritz Securities said auto export tariffs to the United States are expected to be reconfirmed at 15%.