The US President has been granted the moral authority by the God to "take out" North Korean leader Kim Jong-un, a leading pastor has said.

"When it comes to how we should deal with evil doers, the Bible, in the book of Romans, is very clear: God has endowed rulers full power to use whatever means necessary, including war, to stop evil," said Robert Jeffress, Texas megachurch pastor and one of Trump's evangelical advisers who preached a sermon on the morning of his inauguration.

"In the case of North Korea, God has given Trump authority to take out Kim Jong Un," Jeffress was quoted as saying by the Washington Post as saying.

Jeffress said that he was prompted to make the statement after Trump said that if North Korea's threats to the US continue, Pyongyang will be "met with fire and fury like the world has never seen".

The biblical passage Romans 13 gives the government authority to deal with evildoers, Jeffress said. "That gives the government the authority to do whatever, whether it's assassination, capital punishment or evil punishment to quell the actions of evildoers like Kim Jong-un," he said.

Jeffress, who is also an author and a TV host, was critical of former President Barack Obama and claimed Trump will follow through with his threats if it was necessary.

"People instinctively know that this President is not going to draw an imaginary red line and walk around it like President Obama did. I believe we're all going to be forced to soon if North Korea isn't dealt with decisively," he said.

A vocal Republican supporter and advocate of Trump, the senior pastor previously defended controversial plans to build a wall along the border with Mexico.

He compared Trump to the biblical leader Nehemiah who helped rebuild the city of Jerusalem and erected a wall to protect the citizens. In a sermon, he said: "You see, God is not against building walls."

Following Trumps's warning to North Korea, Obama's aide Dan Pfeiffer tweeted: "Don't gloss over the fact that Trump threatened what can only be interpreted as a nuclear attack on North Korea if Kim Jong-un taunts him."

In response to Trump's furious tirade, North Korea said it was "carefully examining" plans to strike Guam island, a US territory in the Pacific southeast of North Korea.