Iran's deputy foreign minister says the situation with its ally Syria is "very complicated" amid growing concern a wider regional war could erupt.
"Fear of war is everywhere in our region," Abbas Araghchi told the BBC.
It comes amid warnings by Israel and the US over Iran's presence in Syria.
Mr Araghchi told the BBC's chief international correspondent Lyse Doucet that Iran was there to fight terrorism, and dismissed warnings about Iran's intentions as "propaganda".
"Just imagine if we were not there. Now you would have Daesh [the Islamic State group] in Damascus, and maybe in Beirut and other places," the minister said.
He deplored the suffering in the Damascus suburb of Ghouta where Syrian bombing in the past few days has killed scores of civilians.
War of drones
Mr Araghchi said Iran was in Syria to fight "terrorist elements" at the invitation of the Syrian government, and its alliance with Syria and the Lebanese militant group Hezbollah aimed to "combat the hegemonic policies" of Israel.
The deputy foreign minister refused to confirm that Iran had sent a drone into Israeli airspace from Syria earlier this month. He said the drone belonged to the Syrian army.
An Israeli warplane targeting Iranian sites in retaliation was shot down by Syrian air defences.
This week Israeli Prime Minister Benjamin Netanyahu brandished what he said was part of the drone at a security conference in Munich and said Iran was the "greatest threat to our world".
But Mr Araghchi said Israel was flying drones over Syria and other neighbouring countries.
"They shouldn't be angry when they are faced with something that they are doing against others on a daily basis," he said.
Nuclear deal at 'critical' moment
Mr Araghchi also said that the 2015 Iran nuclear deal was at a "critical moment" following US threats that sanctions on Iran could be re-imposed.
Iran's deputy foreign minister said he did not believe the deal could survive without the US.
The landmark accord between six global powers and Iran obliges Iran to agree to reduce uranium enrichment activity, dispose of enriched uranium stocks and modify a heavy water facility in return for sanctions to be lifted.
However the White House wants EU signatories to agree permanent restrictions on Iran's uranium enrichment. Under the current deal they are set to expire in 2025. Mr Trump also wants Iran's ballistic missile programme to be addressed.
But Mr Araghchi said the US had to fulfil its side of the deal, formally known as the Joint Comprehensive Plan of Action (JCPOA) before other issues could be discussed.
"Another deal on any other issue depends on how successful is the deal that we have already made, and we have remained fully compliant to that, and the other side has not fully complied," he said.
"If the JCPOA becomes a successful experience for Iran, then they are allowed to ask us for any other issues to negotiate this," he added.
He said Mr Trump's derogatory remarks about the deal were undermining it and this was preventing Iran's economy from improving.
This in turn had contributed to anti-government protests in Iran last month, Mr Araghchi said.
"Peoples' expectations from the JCPOA are not met, it's a fact," he said.
"Most of it is because of this atmosphere of uncertainty which President Trump has created out, around JCPOA, which prevents all big companies and banks to work with Iran, it's a fact, and it's a violation by the United States."