David Cameron has insisted that changing the UK approach to Iran would not provide a "magical key" to solving the Syrian conflict.
The Prime Minister was urged by Labour MPs, including former home secretary Jack Straw, to look carefully at improving relations with Iran following the recent election of Hassan Rouhani as president.
Mr Cameron said talks with Iran had to be approached "very, very cautiously" given its actions in the recent past.
The Prime Minister said to Mr Corbyn:
If you are trying to build a relationship with someone it depends on the actions they take.
Given that the Iranian government was complicit in the complete smashing of our embassy and residence in Tehran, we will want to see some actions so we can build that sort of relationship.
I have reached out by writing to president Rouhani congratulating him on his accession to power and wanting to discuss these issues.
But I said, if we believe there's just some magical key to the Syrian conflict by suddenly adopting a totally different posture towards Iran, I don't think we will be making a very good decision.
Cameron and Miliband avoided any real debate on Syria today in Parliament, as they are both in odd and difficult positions.
For the time being it seems likely we are going to sit this one out and I think you can expect the debate on what that means to run and run.
Number 10 has stated it has "absolutely no plans" to go back to Parliament on the issue of military action against Syria.