Liberal Leader Paul Martin told CBC News he only approved the transcript of a controversial ad suggesting the Tories would post armed soldiers on the streets of Canadian cities.

During a CBC News Town Hall meeting hosted by Peter Mansbridge on Thursday, Martin said the ad was pulled when he saw the finished product and realized it could be misconstrued.

But earlier in the day Martin made no reference of only signing off on the transcript, saying he approved the ad. He said it was pulled "because we felt that there were better ads. That's essentially it."

The ad, which was briefly posted on the Liberal website, features an ominous drumbeat underneath a voice-over that says: "Stephen Harper actually announced he wants to increase military presence in our cities. Canadian cities. Soldiers with guns. In our cities. In Canada."

The ad, which was never broadcast, stems from the Conservative platform which calls for 100 regular troops and 400 reservists to be based in major Canadian cities. But, according to that plan, their purpose would be only for humanitarian means or disaster relief efforts.

Martin said the ad was intended to criticize the Conservatives' policy, saying it would spread soldiers too far apart across the country.

But Mansbridge questioned Martin further about the ad, saying it makes no mention of policy and instead highlights the fact that would be soldiers in Canadian cities with guns.

Martin said it was when he and his campaign team saw the ad, and not just read the transcript, that they realized it was going to be misconstrued.

"When we saw what the ad looked like, it was very clear the message we were trying to convey would not be conveyed by that ad," Martin said.