A senior Chinese foreign ministry official says Beijing cannot rule out the possibility of resuming nuclear tests, if the nuclear arms race between India and Pakistan intensifies.

He stressed that China was committed to the Comprehensive Test Ban Treaty which it signed in 1996, but said the treaty allows signatories to resume testing, if their supreme national security is threatened.

The official, who did not want to be named, said he was particularly concerned by India's recent suggestion that China, and not Pakistan, was the primary security threat to India.

But he assured journalists that China would support efforts to improve relations between India and Pakistan, when the five permanent members of the United Nations security council meet in Geneva on Thursday.