A leading Democrat warned Sunday that the United States and Iran are on a "collision course" as Tehran steps up its nuclear program and escalates hostilities with its alleged plot to kill the Saudi envoy to Washington.

But Dianne Feinstein, the head of the Senate Intelligence Committee, said this was not the time for war with Iran, but for stronger international sanctions to change its behavior, saying she favored sanctions on the Islamic republic's central bank.

"Iran is escalating, I believe, its nuclear development. Iran is increasingly hostile," she said in an interview with Fox News Sunday. "It's a very dangerous situation."

"If you project out a number of years, we are on a collision course. If we want to avoid it, we have to take action to avoid it," she said.

Feinstein said that, like others, she was initially skeptical of the alleged plot by Iran's Quds Force to hire members of a Mexican drug cartel to kill Saudi Ambassador to Washington Adel al-Jubeir, with a bomb in a restaurant.

But after being briefed on the evidence, she concluded it was a "dead bang" case, with compelling intelligence signals and a confession by the Iranian-American used car dealer who was arrested in the plot September 29.

She said there was evidence that Qassem Soleimani, the head of the Quds Force, knew about the plot. Soleimani is believed to report to Iran's supreme leader Ayatollah Ali Khamenei, but Feinstein said there was no evidence Khamenei knew about the plot.

The Quds Force is the special operations arm of the Iranian Revolutionary Guards, and has been accused of using proxies for attacks on US forces in Iraq and as far afield as Argentina, where a truck bombing devastated a Jewish community center in 1994, killing 85.

"Iran reaches out around Iran, but to cross to the other side of the world and try and attack in this country is an escalation, and that's what concerns us and I think that's what concerns the Saudis as well," said Feinstein.

There "could well be" ongoing plots in other countries, she said.

"I don't think this is just an isolated thing that suddenly came up when they have never done these kinds of things before," she added. "They have done these kinds of things before and this is certainly a continuum, but an extension and an escalation."

But when asked whether the United States should go on the offensive against the Quds Force, she cautioned: "It probably would escalate into a war, and the question is: do we want to go to war with Iran at this time? My judgment is no.

"We have our hands full with Iraq, with Afghanistan, with the deteriorating relationship with Pakistan," she said.

"Our country should not be looking to go to war. I think we should be looking to stop bad behavior, short of war," she said.

Feinstein did not elaborate on her other charge, that Iran was escalating its nuclear activities, which the United States suspects is aimed at developing nuclear weapons.

The New York Times reported on Sunday that the US administration is pressing UN nuclear inspectors to make public classified information showing that Iran is designing and experimenting with nuclear weapons technology.

The Times, citing informed officials, said the evidence does not definitively point to the construction of a weapon, but details work on individual technologies essential for designing and detonating a nuclear weapon.

Feinstein said she would support putting sanctions on Iran's central bank, a measure that would blacklist foreign countries or companies that engage in transactions with it.

But that could affect oil prices at a time when the US economy is shaky, she acknowledged. "And maybe that's why they didn't do it. But that makes a big difference."