* Trump says his nuclear button "bigger, more powerful" than North's
* North Korea reopens border hotline it shut down in 2016
* Talks to discuss N.Korea's participation in Winter Olympics
* US downplays talks, urges North to abandon nuclear weapons
The North's decision to open the border phone line came a day after South Korea proposed high-level discussions amid a tense standoff over North Korea's missile and nuclear programmes.
That followed North Korean leader Kim Jong Un's New Year address in which he said he was open to speaking with the South and would consider sending a delegation to the Winter Olympics to be held just across the border in Pyeongchang in February.
US officials said Washington would not take any talks between North and South Korea seriously if they did not contribute to denuclearising North Korea. A State Department spokeswoman said North Korea "might be trying to drive a wedge of some sort".
A South Korean government official checks the direct communications hotline to talk with the North Korean side at the border village of Panmunjom, South Korea. Reuters
Kim ordered the reopening of the hotline at the truce village of Panmunjom at 0630 GMT on Wednesday, when South Korean officials at the border received a call from the North, the South's unification ministry said in a text message.
Officials on both sides were checking the line and conducting a conversation for about 20 minutes, the contents of which were not disclosed by the ministry.
That gesture came only hours after Trump, who has mocked Kim as "Little Rocket Man", again ridiculed the North Korean leader on Twitter.
"Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!" Trump tweeted.
Trump and Kim have exchanged a series of bellicose comments in recent months, raising alarm across the world, with Trump at times dismissing the prospect of a diplomatic solution to a crisis in which North Korea has threatened to destroy the United States.
While appearing to open the door to discussing taking part in the Winter Olympics, Kim also warned that he would push ahead with "mass producing" nuclear warheads in defiance of UN sanctions.
His New Year's Day speech came after a steep increase in missile launches in 2017, as well as the North's sixth and most powerful nuclear test. Kim, who has vowed to develop a nuclear-tipped missile capable of reaching the United States, said he had a nuclear button on his desk.
'Serious and sincere'
The hotline with the South was shut down by North Korea in February 2016 in retaliation against the closing of a border factory town that was jointly operated by the two Koreas.
"We will try to keep close communications with the south Korean side from sincere stand(sic) and honest attitude, true to the intention of our supreme leadership, and deal with the practical matters related to the dispatch of our delegation," the North's KCNA news agency quoted Ri Son Gwon, chairman of North Korea's Committee for the Peaceful Reunification of the Fatherland, as saying.
The talks would aim to establish formal dialogue about sending a North Korean delegation to the Olympics, Ri said.
South Korean presidential spokesman Yoon Young-chan said the North's decision to open the hotline had "significant meaning" because it could lead to constant communication.
US officials had voiced scepticism about the possibility of meaningful talks, particularly if they did not take steps towards banning North Korea's nuclear weapons.
Nikki Haley, the US ambassador to the United Nations, warned North Korea against staging another missile test and said Washington was hearing reports that Pyongyang might be preparing to fire another missile.
Chinese Foreign Ministry spokesman Geng Shuang said both sides should seize the Olympics as an opportunity to improve ties and make concrete efforts toward alleviating tension.
"All relevant sides should grab hold of this positive trend in the Korean peninsula and move in the same direction," Geng told a daily news briefing in Beijing.
North Korea regularly threatens to destroy South Korea, the United States and Japan, and says its weapons are necessary to counter US aggression. The United States stations 28,500 troops in the South, a legacy of the 1950-53 Korean War.
