Iran live updates: Trump: Iran has 'last chance' to sign deal before 'decapitation'

President Donald Trump is claiming that Iranian leaders are being “unbelievably duplicitous” in their public statements about negotiations with the U.S., writing on social media Monday that Iranian leaders “beg” for meetings and then publicly say they won’t have discussions.

"Whether Iran wants to admit it or not, we are, in fact, talking of a solution to a problem that they have caused, for decades," Trump said.

The president’s post comes after he said on Sunday that another round of negotiations would begin on Monday -- though Iran said no talks are underway.

Iranian foreign ministry spokesperson Esmaeil Baqaei reiterated Monday that ongoing talks with Oman are strictly about the Strait of Hormuz and that "the issues related to Iran and the United States should be examined in the next stages to see in which direction the situation will go."

Trump, in his post, appeared frustrated with Iran’s insistence that they’re “only dealing with” Oman.

“Iranian Leadership is unbelievably duplicitous! They ask for a meeting, some would say ‘beg,’ talks begin, with more scheduled in the immediate future, and they say, openly and proudly, that they’re not having any discussions, that nothing is being talked about, and they’re only dealing with ‘Oman,’” Trump wrote.

-ABC News’ Michelle Stoddart and Isabella Murray

Nine ships crossed the Strait of Hormuz on Sunday and 11 ships on Saturday, according to maritime intelligence firm Kpler. Seven of Sunday's nine crossings were conducted via the Iranian route in the northern part of the waterway, Kpler said.

The Bab el-Mandeb Strait -- which sits at the southern entrance to the Red Sea -- recorded 30 crossings on Sunday, down from 37 crossings on Saturday and 42 crossings on Friday, Kpler said.

"The diplomatic outlook is still unsettled. Until U.S., Iranian and Omani signals converge into clear navigation arrangements, operators should treat both chokepoints as contested rather than normalized," Kpler said.

-ABC News' Victoria Beaule

In his weekly press conference on Monday morning, Iranian Foreign Ministry spokesperson Esmaeil Baqaei said that ongoing talks with Oman are strictly about the Strait of Hormuz and that "the issues related to Iran and the United States should be examined in the next stages to see in which direction the situation will go."

"We will have to wait a while to see whether this stage and this process can be connected to another process that leads to a reduction in tension in the region," Baqaei said when asked whether an agreement with Oman was actually the beginning of talks with the U.S.

Baqaei also spoke about the substance of the Strait of Hormuz negotiations, saying talks have focused on agreeing on a single corridor for ships to cross through, rather than the divided northern and southern routes that currently exist.

He also addressed the ongoing diplomatic tensions between Iran and Ukraine after Ukraine struck an Iranian ship in the Caspian Sea a few weeks ago, as part of its campaign to target ships linked to Russia near the Russian coast.

"We will definitely take whatever action is necessary, both to hold Ukraine accountable and to ensure that such a mistake and crime is not repeated by the Ukrainian side again," Baqaei said.

-ABC News' Victoria Beaule

Iranian Foreign Ministry spokesperson Esmaeil Baqaei said in a television interview on Sunday that "under no circumstances" will the Strait of Hormuz return to its pre-war situation, regardless of ongoing talks with Oman, according to a readout published by the state-run IRNA news agency.

Iranian Foreign Minister Abbas Araghchi said on Sunday that negotiations with Oman over the Strait of Hormuz were in their "final stages," but Baqaei said that did not mean that the strategic waterway would be fully reopened as it was before the U.S. and Israel launched their military campaign in February.

"We must ensure that the Strait of Hormuz cannot be misused by parties that have committed aggression against Iran. This requires a mechanism in which Iran's sovereign rights are fully respected," Baqaei said, as quoted by IRNA.

Baqaei said the resumption of fighting in the region had disrupted plans to secure commercial shipping as outlined in the memorandum of understanding signed with the U.S. in June.

"During the first 22 or 23 days of implementing the agreement, the northern route of the Strait was completely secure and ships were passing through it. However, before the end of the 30-day period envisioned for restoring maritime traffic to pre-war conditions, an act of aggression against Iran took place," he said.

After the war disrupted the existing maritime traffic separation scheme in the Strait, ships transiting the area have used either the northern route, which sits along the Iranian coastline, or the southern route along the Omani coastline. Baqaei said that talks with Oman are intended to establish a new route.

Meanwhile, Baqaei said that Tehran will not be pressured by external threats. "Any assumption that threats and media pressure can make Iran retreat from its principled positions is inconsistent with past experience. We will continue to act based on what serves the country's interests," he said.