By Phil Stewart and Idrees Ali
WASHINGTON (Reuters) - North Korea, if left unchecked, is on an "inevitable" path to obtaining a nuclear-armed missile capable of striking the United States, Defence Intelligence Agency Director Lieutenant General Vincent Stewart told a Senate hearing on Tuesday.
The remarks are the latest indication of mounting U.S. concern about Pyongyang's advancing missile and nuclear weapons programs, which the North says are needed for self-defence.
U.S. lawmakers pressed Stewart and the Director of National Intelligence Dan Coats to estimate how far away North Korea was from obtaining an intercontinental ballistic missile(ICBM) that could reach the United States.
They repeatedly declined to offer an estimate, saying that doing so would reveal U.S. knowledge about North Korea's capabilities, but Stewart warned the panel the risk was growing.
"If left on its current trajectory the regime will ultimately succeed in fielding a nuclear-armed missile capable of threatening the United States homeland," Stewart said.
"While nearly impossible to predict when this capability will be operational, the North Korean regime is committed and is on a pathway where this capability is inevitable."
The U.N. Security Council is due to meet on Tuesday behind closed doors to discuss Sunday's test of a solid-fuel Pukguksong-2 missile, which defies Security Council resolutions and sanctions. The meeting was called at the request of the United States, Japan and South Korea.
John Schilling, a missile expert contributing to Washington's 38 North think tank, estimated it would take until at least 2020 for North Korea to be able to develop an ICBM capable of reaching the U.S. mainland and until 2025 for one powered by solid fuel.
But Coats acknowledged gaps in U.S. intelligence about North Korea and the thinking of its leader Kim Jong Un.
He cited technological factors complicating U.S. intelligence gathering, including gaps in U.S. intelligence, surveillance and reconnaissance (ISR), which rely on assets like spy satellites and drone aircraft.
"We do not have constant, consistent ISR capabilities and so there are gaps, and the North Koreans know about these," Coats said.
Washington has been trying to persuade China to agree to new sanctions on North Korea, which has conducted dozens of missile firings and tested two nuclear bombs since the start of last year.
New data on Tuesday showed China raised its imports of iron ore from North Korea in April to the highest since August 2014 but bought no coal for a second month after Beijing halted coal shipments from its increasingly isolated neighbour.
U.S. President Donald Trump has warned that a "major, major conflict" with North Korea is possible over its weapons programs, although U.S. officials say tougher sanctions, not military force, are the preferred option.
Trump's defence secretary, Jim Mattis, said on Friday any military solution to the North Korea crisis would be "tragic on an unbelievable scale."
(Reporting by Phil Stewart and Idrees Ali; Additional reporting by David Brunnstrom; Editing by James Dalgleish)