"At present, we have learned of the relevant situation from some reports ... We are paying attention to such reports," foreign ministry spokeswoman Zhang Qiyue said on Tuesday at a regular briefing.
She added: "We are trying to learn more about the situation." Zhang, however, insisted China was against proliferation of nuclear weapons.
"China's position on this issue is very clear. The Chinese government is firmly opposed to the proliferation of nuclear weapons and supports international non-proliferation efforts," Zhang said.
China has joined international non-proliferation agencies,
including the Nuclear Non-Proliferation Treaty in 1992, but US
intelligence officials concluded years ago that China aided Pakistan in building its first nuclear weapon until the 1980s.
Washington regularly imposes economic sanctions against Chinese companies for selling weapons technology to other countries, including Pakistan.
"China's position on this issue is very clear. The Chinese government is firmly opposed to the proliferation of nuclear weapons and supports international non-proliferation efforts."
Chinese foreign ministry spokeswoman
On Sunday, the Washington Post reported that US officials had found documents which showed dramatic evidence of China's long suspected involvement in Pakistan's nuclear programme.
It said the documents were found in Libya, some of which included text in Chinese, and contained detailed, step-by-step instructions for assembling an implosion-type nuclear bomb that could fit atop a large ballistic missile.
The designs were sold to Libya by a Pakistani-led nuclear
trading network that is now the focus of an expanding international probe, the daily reported.
Zhang on Monday argued that China has been stepping up measures to control weapons exports. "China fulfills and strictly abides by relevant international non-proliferation responsibilities," he said.
"In recent years, China has adopted a series of measures to improve and strengthen export controls."
US President George Bush has
called for expanding the PSI
US Undersecretary of State John Bolton on Monday confirmed
weapons designs were found in Libya but refused to comment on Chinese involvement.
He was visiting China to encourage Beijing to do more to stop the spread of weapons of mass destruction and to discuss the upcoming North Korean nuclear talks, on which Washington and Beijing are working closely.
Bolton's visit was also aimed at garnering China's support for US President George Bush's proposal to expand the so-called Proliferation Security Initiative (PSI), which aims to intercept shipments of arms by land, air or sea.