The US government has lifted an export ban on Anthropic's most advanced artificial intelligence (AI) tools, just weeks after ordering it to restrict access to them over national security concerns, the company has said.

Anthropic said in a statement that it will begin restoring access to Claude Fable 5 and Mythos 5 on Wednesday after being notified that the US Department of Commerce has lifted restrictions on the two models.

They are the firm's most advanced AI tools, which were abruptly suspended on 12 June over concerns that they could be used by hackers to exploit weaknesses in computer systems.

The Commerce Department said in a letter seen by the BBC that Anthropic has addressed the risks.

"Anthropic has agreed to proactively detect and address security risks associated with the models," Commerce Secretary Howard Lutnick wrote in a letter to the tech company.

The firm has also agreed to collaborate on future releases of its AI models and alert the government of any malicious activity, Lutnick wrote.

The Commerce Department reserves the right to reconsider its decision to lift export restrictions if necessary, he added.

The BBC has contacted the Department of Commerce for further information.

Mythos and Fable are two of Anthropic's AI models built on its Claude platform - a rival to the likes of OpenAI's ChatGPT and Google's Gemini.

Fable 5 is a version of the AI model for the consumer market, capable of deep reasoning and can perform complex tasks independently.

Mythos 5 is a version of the platform designed for businesses and cybersecurity experts. It is said to be able to identify vulnerabilities in computer code and exploit them.Both models were released on 9 June.

The firm previously said that US authorities had not pinpointed specific concerns about its technology even as it ordered both platforms to be suspended around the world.

"Our understanding is that the government believes it has become aware of a method of bypassing, or 'jailbreaking' Fable 5," the company said at the time, referring to a process of slipping past software safety restrictions to unblock features.

"However, we disagree that the finding of a narrow potential jailbreak should be cause for recalling a commercial model deployed to hundreds of millions of people."