TAIPEI:   Taiwan's US ties are solid with regular contacts, its foreign minister said on Monday, as the government came under opposition criticism over US President Donald Trump's cool response to the possibility of a phone call with Taiwan's president.

Taiwan President Tsai Ing-wen told Reuters in an interview on Thursday that if the need arose, she would not rule out talking directly again to the US president, when asked about such a possibility.

But later in the day, Trump brushed aside the suggestion, saying he did not want to create problems for Chinese President Xi Jinping when Beijing appears to be helping with efforts to rein in North Korea.

The island's foreign minister, David Lee, responding in a regular parliamentary session to opposition references to Trump's comments, said relations with the United States were good.

"The outlook for Taiwan-US relations is very optimistic," Lee told lawmakers.

Lee said there were "fixed" channels of high-level contacts between the two sides.

He said Taiwan was waiting for the US administration to fill vacancies at senior levels, such as those that handle Asian affairs, to be able to implement bilateral policies.

Trump, as US President-elect, took a congratulatory phone call from Tsai in early December, the first such contact in nearly four decades.

The conversation raised questions about Trump's commitment to the long-standing US position of acknowledging Beijing's cherished "one China" policy, that there is only one China and that Taiwan is part of China.

The December call also infuriated Beijing which fears contacts between Taiwan and foreign governments would confer sovereignty on the island. Democratic Taiwan, self-ruled since 1949, has no interest in being ruled by the autocratic mainland.

Taiwan opposition politicians said Trump's shying away from the possibility of another phone call, in comments in an interview with Reuters, cast doubt in Taiwan on the strength of US ties, even though Taiwan's government has said both sides had communicated on the issue and no phone call was being planned at this stage anyway.

"We heard it and felt very uncomfortable," opposition Nationalist party lawmaker Johnny Chiang said when questioning Lee.

Trump, after raising doubts about his stance on the "one-China" policy, agreed in February to honour it. He played host to Xi at his Florida resort in April and later said he established a good relationship with him.

Taiwan ruling party lawmaker Liu Shyh-fang said Trump was the most difficult ever US president to predict.

"His only policy is: Hard to predict."