Four countries last year prevented Syria from receiving equipment that could be used to test ballistic missile components, a senior US official said on Wednesday.

US national security adviser Stephen Hadley described the previously undisclosed incident in a speech to members of the Proliferation Security Initiative, a network of countries that seeks to stop illicit weapons of mass destruction shipments.

The Bush administration has portrayed the PSI effort, which was launched five years ago and has more than 90 nations as members, as a significant success in its drive to prevent biological, chemical or nuclear terrorism. Analysts say it is hard to judge its effectiveness because members are reluctant to disclose successes to avoid betraying sources that provide intelligence needed to stop shipments. ....