Iran has issued a warning that “serious disagreements” between itself and the US could derail efforts to revive the 2015 nuclear deal following Oman indirect talks. Officials from Iran expressed frustration over what they considered Washington’s refusal to make necessary concessions.

Iran’s Foreign Ministry issued a statement on Sunday noting that recent negotiations had made some technical advances but critical political gaps remain unaddressed. There remain serious disagreements that threaten to derail negotiations unless quickly addressed, the statement read.

Omani mediation efforts aimed to bridge key differences on key issues related to Iran’s uranium enrichment program, lifting of U.S. sanctions and assuring against future breaches of agreement. Both sides had earlier hinted at some progress; however Iran’s latest comments highlight how tenuous negotiations remain.

Iran officials accuse the U.S. of failing to offer credible assurances that Washington won’t withdraw from the deal as they did under former-President Donald Trump, leaving Iran vulnerable. Tehran demands full removal of sanctions that hamper oil exports and banking sector before agreeing to any nuclear concessions.

U.S. officials continue to assert that Iran must first demonstrate compliance with nuclear restrictions before wider sanctions relief can be considered. Furthermore, President Biden is under considerable political pressure not to make concessions that might be seen as too generous towards Tehran.

“The American side remains stuck in its approach of maximum pressure,” an unidentified Iranian negotiator stated to local media outlets. Without real changes to their approach, lasting agreements seem unlikely.

Regional observers believe Iran’s warning could be used as a negotiating tactic in talks reaching a critical phase, with no agreement reached by May closing off diplomatic channels and increasing risk of further instability across the Middle East.

The European Union, which assisted with mediating previous versions of this deal, has encouraged both sides to demonstrate “flexibility and urgency” so as to maintain diplomatic efforts and avoid any potential breakdown.

At present, the fate of nuclear negotiations remains uncertain, with both Tehran and Washington returning home to assess their positions further and consider ways in which diplomacy might survive an ever widening divide in coming weeks.