The UK is to push for more sanctions against North Korea after it claimed to have tested its first nuclear weapon, Margaret Beckett has said.
She said the test, reportedly held at 0236 BST, was "highly irresponsible" and underlined the threat nuclear weapons posed to the world.
Tony Blair condemned the test, which he said showed North Korea's "disregard" for international concerns.
But North Korea has hailed the underground test a success.
Seismic events at a suspected test site were detected by both the US and South Korea.
In a statement, Mrs Beckett said the test was a "highly irresponsible and provocative act by North Korea" which had left the country "isolated".
"The world is united in condemnation. North Korea's action is in total defiance of the whole of the international community," she said.
"For our part the United Kingdom will be pushing for a robust response under chapter seven of the UN Charter", she said, adding that this meant, "we shall be pushing for sanctions against North Korea".
Mrs Beckett said sanctions were already in existence which prevented states transferring missile-related items to or from North Korea.
"Any new sanctions clearly have to go further than this," she said.
Britain would continue to work with its partners on the UN Security Council to take forward the international community's response, she added.
"It should be clear to North Korea that it must return to the six-party talks and stop disregarding the concerns of its neighbours and of the international community."
Earlier Mr Blair said: "I condemn this completely irresponsible act by the government of the DPRK (Democratic People's Republic of Korea).
"The international community has repeatedly urged them to refrain from both missile testing and nuclear testing.
"This further act of defiance shows North Korea's disregard for the concerns of its neighbours and the wider international community."
Mrs Beckett has rejected suggestions North Korea's actions had anything to do with military action against Iraq or that Britain's moral authority had been weakened by the Iraq war.
"I don't think that is the case," she told BBC Radio 4's Today programme.
"After all, it's quite a considerable time now since that happened and there are much more current United Nations statements, resolutions and so on."
The Foreign Office said the international community would react "robustly" to the test.
A spokesman added: "This nuclear test is viewed by the UK, and will be viewed by the rest of the international community, as a highly provocative act to which we will respond robustly.
"It will raise tensions in an already tense region and have repercussions internationally."
A White House statement said such a test would be a "provocative act", while China denounced it as "brazen".