Washington, Dec 13 (IANS): US Secretary of State Rex Tillerson has said that the US embassy in Israel was unlikely to move to Jerusalem before 2020.

"It's not going to be anything that happens right away," Tillerson said in a speech at the State Department on Tuesday. "Probably no earlier than three years out, and that's pretty ambitious."

US President Donald Trump formally recognised Jerusalem as the Israeli capital last week but he nevertheless signed a national security waiver which will allow him to delay the movement of the embassy to Jerusalem from Tel Aviv for an additional six months.

Administration officials said there were functional and logistical reasons the US cannot open a new embassy any time in the near future, the New York Times reported.

Speaking of the moving of the US embassy, Trump had said the State Department will immediately begin to hire architects and engineers so as to make the new embassy "a magnificent tribute to peace" when completed.

Trump's decision, which was seen as undermining the Middle East peace process and further destabilizing the region, has drawn condemnation and opposition globally.

Tillerson also spoke about North Korea at a policy forum here. He said the US was ready to open nuclear disarmament talks with North Korea without preconditions, CNN reported.

"We've said from the diplomatic side, we're ready to talk anytime North Korea would like to talk," Tillerson said, in what amounted to a direct public invitation for Pyongyang to put aside an escalating cycle of tests and taunts and engage in diplomacy.

"Let's just meet and let's talk about the weather if you want and talk about whether it's going to be a square table or a round table if that's what you're excited about.

"Then we can begin to lay out a map, a road map, of what we might be willing to work towards," the US Secretary of State said.

But he insisted that there needed to be a "period of quiet" first, without any nuclear or missile tests.

He added that economic and diplomatic sanctions would continue until "the first bomb drops", and Trump still wanted China -- Pyongyang's main economic ally -- to cut off oil supplies to North Korea.

Tillerson said China had made contingency plans to accommodate North Korean refugees in the event of a conflict.

Meanwhile, North Korean state media on Wednesday said Kim Jong-un had vowed his country would become "the strongest nuclear and military power in the world".