UPDATE 2-China's imports from N.Korea plummet in December, lowest for 4 years

* China Dec imports from North Korea -81.6 pct y/y to $54.34 mln

* China Dec exports to North Korea -23.4 pct y/y to $260 mln

* China 2017 imports from North Korea -33 pct to $1.72 bln

* China 2017 exports to North Korea +8.3 pct to $3.34 bln (Adds comments from expert at state-backed research institute)

BEIJING, Jan 12 (Reuters) - China's imports from North Korea plunged in December to their lowest level in dollar terms since at least the start of 2014, with trade curbed by U.N. sanctions aimed at persuading North Korea to abandon its ballistic missile and nuclear weapons programs.

Imports from North Korea slumped 81.6 percent year-on-year to $54.34 million, Huang Songping, Chinese customs spokesman, said in a briefing in Beijing on Friday. That's the smallest monthly value since at least January 2014.

Chinese customs will formally release data for trade with North Korea in the second half of the month, along with a breakdown by product.

The United Nations began imposing sanctions on North Korea in 2006, but tougher measures were invoked in 2017 as tensions flared anew over the country's nuclear and missile programs.

The penalties that came into force on Sept. 5 last year banned countries from buying coal, iron ore, lead, lead ore and seafood from North Korea.

In November, China imported no iron ore, coal or lead from North Korea, the second full month of the U.N. trade sanctions.

"In terms of how big of an impact it (falling trade) had on North Korea, there was definitely impact because some of their products could only go to China while others could only be imported from China," said Chen Fengying, an economics expert at state-backed China Institutes of Contemporary International Relations.

"You have to understand it was the most tense period for bilateral ties, and foreign relations determine trade relations."

China, the main source of North Korea's fuel, did not export any gasoline, jet fuel, diesel or fuel oil to its neighbor in November.

China's exports to North Korea in December declined 23.4 percent from a year earlier to $260 million, Huang told reporters.

Compared with a month earlier, exports fell 9.7 percent.

In November, China stopped exporting oil products to North Korea, after the U.N. Security Council that month imposed new caps on trade with North Korea, including limiting oil product shipments.

For 2017, China's imports from North Korea dropped 33 percent to $1.72 billion, the lowest value in at least four years.

However, exports to the country rose 8.3 percent to $3.34 billion. The value was the highest since 2014.

Non-commodities that China exports to North Korea included electronics, plastic products and garments. (Reporting by Yawen Chen, Stella Qiu and Ryan Woo; Editing by Simon Cameron-Moore & Shri Navaratnam)