Iran's Revolutionary Guards say Saudi Arabia was behind twin attacks in Tehran that killed at least 12 people and injured 43.

"This terrorist attack happened only a week after the meeting between the US president (Donald Trump) and the (Saudi) backward leaders who support terrorists. The fact that Islamic State has claimed responsibility proves that they were involved in the brutal attack," said the statement, published by Iranian media on Wednesday.

Attackers dressed as women burst through parliament's main entrance in central Tehran on Wednesdau, deputy interior minister Mohammad Hossein Zolfaghari said, according to the semi-official Tasnim news agency.

"One of them was shot dead and another one detonated his suicide vest," he said.

About five hours after the first reports, Iranian news agencies said four people who had attacked parliament were dead and the incident was over.

At least 12 people were killed by the attackers, the head of Iran's emergency department, Pir-Hossein Kolivand, was quoted as saying by state broadcaster IRIB.

Islamic State claimed responsibility and released a video purporting to show gunmen inside the parliament building. It also threatened more attacks.

Earlier on Wednesday the deputy head of Iran's Revolutionary Guards promised retaliation on Islamic State and its allies.

"Let there be no doubt that we will take revenge for today's attacks in Tehran, on terrorists, their affiliates and their supporters," Brigadier General Hossein Salami was quoted as saying by state media.

The Revolutionary Guards also said in a statement published on state media that it "has proved in the past that it will take revenge for all innocent blood shed" in Iran.

Iran's supreme leader, Ayatollah Ali Khamenei, dismissed the attacks as mere "fireworks" that would not weaken the country's fight against terrorism, state TV reported.

"These fireworks have no effect on Iran. They will soon be eliminated ... They are too small to affect the will of the Iranian nation and its officials," he said.

Speaking in Berlin, Foreign Minister Adel Al-Jubeir said there was no evidence to implicate Saudi Arabia in the attacks, which is Riyadh's arch regional rival.

"We condemn terrorist attacks anywhere they occur and we condemn the killing of the innocent anywhere it occurs," Jubeir said.
The US condemned a militant attack in the Iranian capital.

"The United States condemns the terrorist attacks in Tehran today," said a State Department spokeswoman. "The depravity of terrorism has no place in a peaceful, civilised world."

United Nations Secretary-General Antonio Guterres also condemned the attack.

"The Secretary-General hopes those responsible for this unjustifiable violence will be swiftly brought to justice. All countries must work together in fighting terrorism while upholding the universal rights and values that bind the global community," UN spokesman Stephane Dujarric told reporters.