Afghan women wear blue scarves, symbolizing justice, on their heads during a ceremony to mark International Women's Day on March 8, 2009, in Kandahar province, Afghanistan. (Allauddin Khan/Associated Press)

Prime Minister Stephen Harper said Wednesday that Canada remains committed to its mission in Afghanistan, but he voiced strong concerns about new Afghan legislation that would limit women's rights in that country.

"This is antithetical to our mission in Afghanistan," Harper said in an interview with CBC News.

The new Afghan family law would reportedly make it illegal for women to refuse their husbands sex, leave the house without their permission or have custody of children.

Prime Minister Stephen Harper, speaking in London, England, on Wednesday, says he's 'deeply troubled' by Afghanistan's new family legislation. (Adrian Wyld/Canadian Press)

"We're deeply troubled by it. And I don't think we're by any means alone," the prime minister said during an interview in London ahead of the G20 talks that begin on Thursday.

"Making progress on human rights for women is a significant component of the international engagement in Afghanistan. It's a significant change we want to see from the bad old days of the Taliban," he said.

"I think President [Hamid] Karzai and those other actors who may be supporting this policy will find themselves under considerable pressure," Harper said.

Karzai's office has so far refused to comment on the legislation, which has been criticized by some Afghan parliamentarians and a UN women's agency but has not yet been published.

The proposed legislation became a focus of concern in question period in Ottawa Wednesday.

"After all the sacrifices, after all that Canadian families have put on the line, could this really end up being what we are fighting for?" B.C. New Democrat MP Dawn Black asked.

International Trade Minister Stockwell Day repeated the government's position, saying "we are very concerned with the provisions in this law."

Critics slam law

Critics say the Afghan government approved it in a hurry to win support in the upcoming election from ethnic Hazaras — a Shia Muslim minority that constitutes a crucial block of swing voters.

Harper noted that Canada was reluctant to get drawn into any Afghan electoral politics, but said: "The concept that women are full human beings with human rights is very, very central to the reason the international community is engaged in this country."

Earlier in the day, Harper told Britain's Sky TV that Canadian forces have borne a significant burden in the region.

"Canada has had, per capita, by far the highest casualties in Afghanistan," he said. "We are in Kandahar, [which is,] next to Helmand, the most difficult province in the country."

PM 'optimistic' heading into G20 talks

On the global economy, Harper told CBC that he was "optimistic" heading into the G20 meetings.

"We're virtually all in the same boat here. There are geopolitical rivalries obviously among some of the players around the table on other matters.

"But to the extent that we are — most of us — now all part of a genuinely global economic system and global trading arrangement we should all view ourselves as solutions to a global problem," he said.

The prime minister praised U.S. President Barack Obama's leadership skills. "He's a great talker but he's also a great listener," Harper said.

"In the end, he's going to have to set a direction — and the direction won't be effective unless all of us, having got our input, then are prepared to actually work together and be part of a global solution."

Also Wednesday, Harper took part in the customary visit by a Canadian prime minister to Buckingham Palace where he met with the Queen and also with Prince Charles.

The prime minister also named Kevin MacLeod as the new Canadian Secretary to the Queen, a position that, among other things, helps co-ordinate royal visits to Canada.

"I am delighted that Her Majesty the Queen of Canada has graciously agreed to this appointment," the prime minister's office said in a media release.