North Korea does not yet have an operational missile that could hit the continental US, a US report says.
North Korea raised concerns with a missile test in early March
But its weapons could target South Korea and Japan, and it is working on a longer-range solid-fuel missile.
Missile exports were a significant source of foreign exchange for the country, the report by the Center for Nonproliferation Studies also said.
Concerns over North Korea's weapons programme rose this month when it test-fired two short-range missiles.
A US military official told a government committee that the missiles represented a "leap forward" for Pyongyang's programme in terms of reliability and accuracy.
The report by the California-based NGO said that North Korea did not currently have "an operational missile" to strike the US.
The longer-range Taepodong-X missile could theoretically reach Alaska, Hawaii and parts of the coastal US, US officials believe, and an untested third version, Taepodong 2, could potentially strike further into the country.
But the report said the missile would not be accurate and the payloads it could carry would be militarily insignificant.
"North Korea has not demonstrated the capability to make a nuclear weapon small enough to be part of a missile warhead," the report said.
Pyongyang would require "several years" to produce a reliable missile system that could deliver a nuclear warhead to the US, it said.
Exports to Iran
But the NGO said North Korea had more than 800 ballistic missiles and could reach South Korea and Japan with possible biological and chemical payloads.
It has a Scud-type missile with which it could target all of South Korea, and it has missiles with a range of 1,000 km (625 miles) with which it could strike Japan.
The report also highlighted Pyongyang's missile exports.
Map shows range of Taepodong 1 missile, flown over Japan in 1998. Range 1,500-2,000 km, payload: 1,000 kg
Evidence that North Korea working on testing Taepodong 2 with range up to 6,000 km
Evidence from Jane's Defence of a pair of new ballistic missiles - one sea-based
Other: Scuds B, C and D: Range from 300-700 km, payload 500-1,000 kg
Nodong: Range 1,000 km, payload 700 kg
"North Korea's earliest and most loyal customer for missiles and missile technology has been Iran," it said.
North Korea has conducted other missile tests in the past.
In May 2005, it fired a short-range missile 100km (62 miles) into the Sea of Japan and in 1998 it flew a Taepodong-1 missile over Japan.
The report comes as six-nation talks over North Korea's nuclear programme are deadlocked.
Last September, North Korea agreed to give up its nuclear goals and return to the nuclear non-proliferation treaty.
But demands that it be given a civilian nuclear reactor and a row over US financial sanctions have brought talks to a standstill with no date set for more negotiations.