The United Nations chief stepped up efforts on Friday to persuade eight holdout states to ratify a 1990s treaty to ban nuclear weapon tests, and said governments were now spending vast amounts on building arsenals of death.

More than 150 countries have so far ratified the Comprehensive Nuclear Test Ban Treaty (CTBT) but the United States, China, India, Pakistan, Israel, Iran, North Korea and Egypt must also do so before it can become international law.

It is distressing that this treaty has yet to enter into force, U.N. Secretary General Ban Ki-moon told a conference on the pact in Vienna, where its Preparatory Commission is based.

Any country opposed to signing or ratifying is simply failing to meet its responsibilities as a member of the international community.

Ban said he was ready to meet leaders of those states which are still reluctant or may have doubts about the ratification of the test ban treaty, which was negotiated in the 1990s but has yet to take force.

India, Pakistan, North Korea and Israel are outside the nuclear Non-Proliferation Treaty, the 1970 pact aimed at preventing the spread of nuclear weapons. Iran is part of the NPT but the West accuses it of seeking to develop a capability to build atomic bombs. Tehran denies the charge.

The United States and China are among the world's five recognised nuclear weapons states, together with Russia, France and Britain.

Proponents say U.S. ratification of the pact, rejected by lawmakers in 1999, could encourage other holdouts to sign.

It is irresponsible to see this treaty still waiting to come into effect 15 years after it was opened for signature, Ban said, without naming the eight states. Governments now spend vast sums of money to build and test arsenals of death.

The administration of U.S. President Barack Obama said in May last year that it was preparing a push for approval of the treaty, arguing that Washington no longer needs to conduct such tests but does need to stop other countries from doing so.

But it has not given a precise time when it would seek a Senate vote on the treaty, which the chamber rejected when fellow Democrat Bill Clinton was president in the 1990s. A two-thirds majority would be needed for approval.

Obama, who will seek a second term this year, has made clear he sees the test ban pact as a step toward his vision of a world without nuclear weapons, such as the new START arms reduction treaty the Senate approved last year.

At the time of the Senate vote in 1999, opponents argued that a permanent end to testing could erode the reliability of the U.S. nuclear arsenal. The country last carried out a test nearly 20 years ago.

Some also questioned whether cheaters could be detected.

Ban said: There is no good reason to avoid signing or ratifying this treaty.

(Reporting by Fredrik Dahl; Editing by Mark Heinrich)