Sir Keir Starmer has denied giving “false hope” to Port Talbot steel workers ahead of the planned closure of the town’s last blast furnace next month.
The Labour UK government is in discussions to try to save jobs at Tata Steel, where thousands face redundancy.
The prime minister said the Labour UK government will do “everything we can” but added: “I’m not going to pretend it’s anything other than tough.”
He was speaking to journalists at a windfarm in Carmarthenshire, as part of a two day trip to Wales.
He met Eluned Morgan in Cathays Park, in Cardiff, for his first meeting with her since she became first minister on Monday.
Sir Keir claimed to have “turbocharged” the party’s action on steel since he has been in power.
Asked if he was risking giving false hope to Port Talbot steel workers, he said: “No.
“We’re working really hard on this, both the first minister and myself jointly on this, because it’s so important we do everything we can to preserve those jobs.”
He later added: “I don’t want to give anybody false hope. I’m not going to give up on trying to preserve as many jobs as we can.
“I’m not going to give up on making sure that those in the supply chains have the money they need to diversify, where they need to diversify, which is why we put money behind this just seven days ago.
“It is very important that we have steel production here in south Wales, very important that the government is committed to that.