Tony Blair appeared to cast doubt on Clare Short's future as a Labour MP after she accused the UK of bugging the UN Secretary General's office.
Blair says he regrets Clare Short's comments
He said he believed her allegations were "completely irresponsible" and regretted the way she had dragged the security services "through the mud".
"People who put them in the firing line like this, I really do not have a great deal of respect for," he said.
He was addressing his monthly news conference after Ms Short's remarks.
The former international development secretary said she had read transcripts of some of the conversations UN Secretary General Kofi Annan had had in the run up to war with Iraq.
"The UK in this time was also getting spies on Kofi Annan's office and getting reports from him about what was going on," she told BBC Radio 4's Today programme.
"These things are done and in the case of Kofi's office, it was being done for some time."
Ms Short said she had recalled thinking that people would be able to read transcripts of her own conversations with Mr Annan.
Asked to confirm if British spies were instructed to carry out operations within the UN on people like Mr Annan, she said: "Yes, absolutely."
Quizzed about Ms Short's comments during his monthly meeting with reporters at Downing Street, Mr Blair said he did not have any plans to talk to his ex-minister.
"I also haven't had an opportunity to consider any questions and issues to do with discipline," he said.
But pressed further about Ms Short's future as an MP, Mr Blair said: "These are issues that I will have to reflect upon. This has happened this morning. There will obviously be issues that arise."
He said "to be fair", Ms Short had done a good job during her time as international development secretary - a post she quit after the UK went to war with Iraq.
While he would not comment on the work of Britain's security services, he urged people not to take this as an indication that Ms Short's allegations were true.
"I really do regard what Clare Short has said this morning as totally irresponsible, and entirely consistent," he said.
"I am sorry that she has said the things that she's said, but she must know, and I think everyone knows, you can't have a situation where people start making allegations like this about our security services.
"It is completely irresponsible ... This is a dangerous time for this country and the world.
Tony Blair said Ms Short's comments 'were wrong'
"We need our security services. We need these people who risk their lives for us to feel confident of the strong support and backing right across the political spectrum for what they do.
"I give them that strong backing - I think they do a fantastic job.
"I really regret the way they have been dragged through the mud over the past few months. It is totally unfair for them ...
"People who put them in the firing line like this - I really do not have a great deal of respect for ...
"It's just a pity she's done what she's done today because I think it is wrong."