The Harper government is maintaining its unyielding isolation of Iran even as the United States and Britain explore how to enlist Tehran's help in defusing the Iraq crisis.

Britain says it will re-open its embassy in Tehran while the U.S. is looking at other possible areas of co-operation in an effort to stop the violent offensive by militants across Iraq.

British Foreign Secretary William Hague says the circumstances are right to re-open the embassy, which was closed in 2011 after it was attacked and ransacked.

Canada followed suit in 2012, shuttering its embassy in the Iranian capital and kicking out the country's diplomats.

A spokesman for Foreign Affairs Minister John Baird says Canada's relations with Tehran will remain severed until Iran can prove it is trustworthy.

Baird's office says Canada respects the decisions of its allies, but its position is rooted in principle.