Canada will extend its air strike campaign against Islamic State (IS) into Syria, Prime Minister Stephen Harper has announced.

"In our view, ISIL [IS] must cease to have any safe haven in Syria," Harper said in the House of Commons.

Canada's mission against ISIS will also be extended for one year, beyond October's election and well into 2016.

Opposition leaders have criticised Harper for drawing Canada into a war with unclear objectives.

The move means Canada will be the first Nato country, other than the United States, to strike inside Syria.

ISIS controls vast swath of land on both sides of the Iraq-Syria border.