Japanese Foreign Minister Nobutaka Machimura has again warned North Korea to return to nuclear talks or face being taken to the UN Security Council.
There are fears North Korea may be about to test a nuclear bomb
He was speaking on the sidelines of an Asia-Europe meeting (Asem) being held in the Japanese city of Kyoto.
The warning came amid fresh reports of intelligence suggesting North Korea may be preparing to test a nuclear weapon for the first time.
The North has shunned six-nation talks on its nuclear plans for almost a year.
"If there is no progress, we have to think of other options, such as taking this matter to the United Nations Security Council," Mr Machimura told reporters after meeting his South Korean counterpart, Ban Ki-moon.
Analysts say that taking North Korea to the UN could result in international sanctions against the impoverished nation. They say a key deadline may be the end June, which would mark one year since Pyongyang took part in the talks.
North Korea has repeatedly said it would consider sanctions tantamount to a declaration of war.
Mr Machimura was speaking amid mounting concern that North Korea might be preparing a nuclear weapons test.
The New York Times reported on Friday that US officials were assessing satellite photographs that appeared to show extensive preparations for a test, which would confirm North Korea's claim to have developed nuclear weapons.
The newspaper said photographs suggested the digging and filling in of a tunnel in the country's remote north east, and the construction of a viewing stand.
Analysts cautioned, however, that assessing North Korea's real intentions is always difficult, and satellite photographs have been unreliable in the past.
The BBC's Seoul correspondent, Charles Scanlon, says some analysts point out that the North Koreans could also be bluffing, putting on a show for the benefit of US satellites to strengthen its negotiating position.
Russia, North Korea's neighbour, has responded to the latest rumours about a possible test by sending a parliamentary delegation to Pyongyang.
"Information has been conveyed from North Korea that hints that North Korea will conduct a nuclear test. We are taking it seriously," Konstantin Kosachev, chairman of the Duma, told Japanese television.
North Korea has also rattled nerves in recent days by testing a short-range missile over the Sea of Japan [East Sea] last weekend, and shutting down its nuclear reactor at Yongbyon. There are fears this is in order to extract more weapons-grade plutonium.
Earlier on Friday, South Korean Foreign Minister Ban Ki-moon tried to persuade his Chinese counterpart, Li Zhaoxing, to use Beijing's influence on North Korea to bring it back to the talks table.
But according to Park Joon-woo, South Korea's director general in charge of Asia and Pacific affairs, Mr Li stressed China's influence was "limited".
North Korea is believed to have a handful of nuclear weapons and to have the capacity to produce more.
In February it publicly declared itself a nuclear power, and said it was suspending its participation in talks over its nuclear programme for an "indefinite period".