Iranian President Hassan Rouhani said on Saturday new US sanctions on some Iranian and foreign banks and businesses were "unconstructive" and against the spirit of Tehran's nuclear negotiations with world powers.

But he added at a news conference in Tehran that he was not pessimistic about the continuation of the discussions and that Iranians and their leadership were united behind the effort to settle a decade-old dispute about Iran's nuclear programme.

The United States on Friday penalized a number of Iranian and other foreign companies, banks and airlines for violating sanctions against Tehran largely tied to its nuclear work.

Washington said it was sending a signal that there should be no evasion of the sanctions while international talks continue on relaxing them if Iran agrees to curb its nuclear activities.

Asked for his reaction, Rouhani said: "They are in conflict with the spirit of talks. They are unconstructive in my opinion."

In remarks quoted by the state news agency IRNA, Foreign Ministry spokeswoman Marzieh Afkham said such actions "put into question the seriousness, honesty and good faith of negotiations with the US"

However Rouhani also struck a more positive tone later in the news conference, suggesting there was hope of reaching a deal by the November 24 deadline.

"It is tough but I'm not pessimistic about the continuation of the talks," he said.

"Our nuclear negotiating team should not feel alone. The Iranian nation, leader and my government are behind them."

Iran and the United States, France, Germany, Britain, China and Russia failed to meet a July 20 deadline to negotiate a comprehensive agreement under which Iran would curb its nuclear activities in exchange for the easing of economic sanctions that have crippled its economy.

The new deadline was extended to November 24. Members from all parties are set to meet on the sidelines of the UN general assembly in New York, Rouhani said.-Reuters