A man charged with planning terrorist explosions targeting Britain's electricity network, a nightclub and a major shopping mall refused to continue testifying Monday, saying he feared it would cause difficulties for his family in Pakistan.

Asked by his lawyer, Joel Bennathan, about his purchase of 1,300 pounds of ammonium nitrate fertilizer, which can be used to make a bomb, 24-year-old suspect Omar Khyam said he would not testify.

"Before we go on to that topic, I just want to say the ISI (Pakistani secret services) in Pakistan has had words with my family relating to what I have been saying about them," said Khyam, the first of the seven defendants to testify at their trial.

"I think they (the ISI) are worried I might reveal more about them, so right now, as much as I want to clarify matters, the priority for me has to be the safety of my family, so I am going to stop.

"I am not going to discuss anything related to the ISI any more or the evidence."

The trial was adjourned for an hour while lawyers conferred about the development.

When the session resumed, Judge Michael Astill warned Khyam: "If you refuse to answer questions, the jury may draw such inferences as appears proper from your failure to do so."

Khyam answered "yes" when asked if he understood.

The trial did not resume, and proceedings were suspended for the day.

Khyam and the other suspects were arrested in 2004, during an operation in which police seized the 1,300 pounds of ammonium nitrate fertilizer.

Khyam, his brother Shujah Mahmood, 19, Waheed Mahmood, 34, Jawad Akbar, 23, Salahuddin Amin, 31, Anthony Garcia, 24, and Nabeel Hussain, 21, deny conspiring to set off explosions likely to endanger life between Jan. 1, 2003, and March 31, 2004.

Khyam, Garcia and Hussain also deny a charge under the Terrorism Act of possessing the fertilizer for terrorism. Khyam and Shujah Mahmood also deny possessing aluminum powder for the purposes of terrorism.