OTTAWA (Reuters) - Canada said on Wednesday it was pressing ahead with plans to issue tamper-proof identification cards to immigrants in a bid to quash the rampant fraud of immigration documents.

Immigration Minister Elinor Caplan said it was clear major changes were needed to the current system, whereby immigrants granted the right to live permanently in Canada are issued with a simple form to staple into their passports.

"We see tremendous fraud in immigration documents," she told reporters in Ottawa.

"We're very aware that since the (invention) of the photocopier and the color photocopier that our documents are open to fraudulent use and we want to stop that," she said.

Canada, with a population of 31 million, is one of the few countries in the world still accepting large numbers of immigrants. In February it lifted its annual target range from 225,000 to 235,000. Eventually it wants to attract around 300,000 immigrants a year.

Caplan admitted there was a problem with fraud but dismissed critics who say the system is so vulnerable that up to 200,000 people could be living in Canada illegally.

"There is no evidence to suggest that there are 200,000 people living illegally in Canada...we estimate that it's probably between 18,000 and 20,000," she said.

Officials are still developing the new cards and Caplan would not say when they might be introduced.

"We think technology is available so we can have a more secure document, which will help people who have legitimate status in Canada," she said.

"They would present the card at a port of entry, which would speed their entry so they are not hassled at the border when they return to Canada."

In a separate development, officials at Canada's Passport Office said they were working on plans to make the country's passports more difficult to forge.

Neville Wells, of the office's security division, said the passports were already extremely difficult to counterfeit accurately. The passport was last designed in the early 1990s.

"We're working on it and we're hoping to come up with something quite new in the fairly near future. I'm not going to announce a time because we don't have it," he told Reuters, saying the Passport Office aimed to change the design roughly every five years.

"It's time to do something new. Any passport issuing authority will tell you that every once in a while you have to do something because no matter what you do, the bad guys will try to find a way to defeat your system," he said.