Looking for His glorious appearing! Titus 2:13

New York: Iraq has received "credible" intelligence that Islamic State militants plan to attack subway systems in Paris and the United States, Iraq's prime minister said on Thursday, but senior U.S. officials said they had no evidence to back up the claim.

Prime Minister Haider al-Abadi said he had received the information Thursday morning from militants captured in Iraq and concluded it was credible after asking for further details. The attacks, he said, were plotted from inside Iraq by "networks" of the Islamic State, also known as ISIS or ISIL.

"They plan to have attacks in the metros of Paris and the US," Abadi told a small group of US reporters while in New York for the annual meeting of the UN General Assembly. "I asked for more credible information. I asked for names. I asked for details, for cities, you know, dates. And from the details I have received, yes, it looks credible."

Barack Obama meets with Iraqi Prime Minister Haider al-Abadi during the UN General Assembly in New York on Wednesday. On Thursday, Abadi spoke of a 'credible' terrorist plot to target subways in the US and Paris. Photo: Reuters

National Security Council spokeswoman Caitlin Hayden said the White House had not confirmed any plan to attack the US and French subway systems. "We have not confirmed such a plot, and would have to review any information from our Iraqi partners before making further determinations," she said.

Two senior US security officials, contacted following the comments from Abadi, said the United States had no information to support the threat.

New York Governor Andrew Cuomo said authorities had already begun to beef up security at New York City's mass transit sites before Abadi's comments. The New York City Police Department said it was aware of the prime minister's warning and in close contact with the FBI and other agencies to assess the threat.

There is 'credible' information that Islamic State jihadists plan to attack train systems in Paris and the US, according to Iraqi Prime Minister Haider al-Abadi. Photo: AP

There had been no credible threats made against Washington DC's rail and bus system, Washington Metro spokesman Dan Stessel said in an email.

The United States and France have both launched air strikes against Islamic State targets in Iraq as part of a US-led campaign to "degrade and destroy" the radical Sunni militant group, which has seized a third of both Iraq and Syria.

Abadi disclosed the intelligence while making a case for Western and Arab countries to join that campaign. "We want to increase the number of willing countries who would support this," he said. "This is not military. This is intelligence. This is security. The terrorists have a massive international campaign. Don't underestimate it."

Air cover ... US Navy F/A-18F Super Hornet lands aboard the aircraft carrier USS George H.W. Bush in the Persian Gulf. Photo: AP

In the past, the United States had received threats that various militant groups were targeting transportation systems but there is no recent information about an imminent plan by Islamic State, one US official said, speaking on the condition of anonymity.

Cuomo said the enhanced security in New York was part of a bi-state initiative announced on Wednesday with New Jersey Governor Chris Christie, in response to possible threats by Islamic State militants.

Abadi also said that Iraq did not want to see foreign "boots on the ground," but stressed the value of providing air cover for the country, saying that the Iraqi air force did not have sufficient capability.

He said that Australia was "very interested" in participating, though he did not provide details. He also voiced optimism about a planned British parliament vote on Friday on the matter, saying "they reckon it will be successful."

Earlier on Thursday, France said it would increase security on transport and in public places after a French tourist was killed in Algeria, and said it was ready to support all states that requested its help to fight terror.