Iran can only lose by negotiating with the United States and must be careful to limit any dealings with some "untrustworthy" European states, the Islamic Republic's top leader said on Wednesday.

Tensions ramped up between the United States and Iran after President Donald Trump withdrew from a multilateral nuclear deal last year and reimposed sanctions. The U.S. sanctions are putting unprecedented pressure on Iran, Supreme Leader Ayatollah Ali Khamenei said last month.

Tehran has now turned to the remaining signatories, particularly the European powers - France, Germany, and Britain - to salvage the deal. "With regard to America, no problem can be resolved and negotiations with it have nothing but economic and spiritual loss," Khamenei wrote on his official website.

"Today, the Iranian people see some European countries as cunning and untrustworthy along with criminal America. The government of the Islamic Republic must carefully preserve its boundaries with them." "Iran must not retreat a single step from national and revolutionary values."

Khamenei pointed to sanctions as a big external challenge for the country and added, in an apparent jab at pragmatist President Hassan Rouhani, "weakness in management" was one of the biggest internal challenges. France, Germany and Britain opened a new channel for non-dollar trade with Iran last month to avert U.S. sanctions but top Iranian officials have said that Europe has not done enough to keep the deal intact. 

Iranian Foreign Minister Mohammad Javad Zarif said Wednesday that a 60-nation conference being co-hosted by Washington in Warsaw on Iran and the Middle East was "dead on arrival". "It is another attempt by the United States to pursue an obsession with Iran that is not well-founded," Zarif told a Tehran news conference. "The Warsaw conference I believe is dead on arrival." 

"I think the fact that they are not aiming to issue any agreed text but rather are just attempting to use their own statement on behalf of everybody else shows they don't have any respect for it themselves," he said. 

"You usually don't bring 60 countries and states together in order to speak for them. That indicates to you that they don't believe they have anything to gain from this meeting." 

Much of the schedule for the conference remains vague amid deep divisions over policy towards the region, where Washington has adopted the deep hostility towards Iran of its allies Israel and Saudi Arabia. 

Washington will be represented by both Vice President Mike Pence and Secretary of State Mike Pompeo, but major European allies are sending low-profile delegations amid unease over President Donald Trump's strident calls to strangle Iran's economy. 

The main session will take place on Thursday when Pence, Pompeo and Israeli Prime Minister Benjamin Netanyahu are all scheduled to address the conference. 

Netanyahu, who has vowed to keep striking Iranian forces until they leave war-torn Syria and has not ruled out a military strike to destroy Iran's remaining nuclear facilities, is likely to deliver a fiery address.  

But outside of Israel, Iran's Arab rivals and the Trump administration, nearly all countries still back an accord negotiated under previous U.S. President Barack Obama under which Iran agreed to accept tight limits to its nuclear activities in return for the easing of crippling economic sanctions. 

(Cover: Iran's Supreme Leader Ayatollah Ali Khamenei meets with people of Qom, in Teheran, Iran, January 9, 2019. /VCG Photo)