Protesters chant slogans and hold up posters of Gen. Qassem Soleimani during a demonstration in Tehran. Ebrahim Noroozi/AP

Iran signalled on Sunday it favours "de-escalation" after 10 days of heightened tensions with the United States that saw both sides fire missiles and led Tehran to accidentally shoot down a passenger aircraft.

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Security was stepped up in Iran's capital after a vigil the previous night for those killed in the air disaster turned into an angry protest and police temporarily arrested the British ambassador for being there.

US President Donald Trump gestures at a meeting. File photo

US President Donald Trump meanwhile warned Iran against harming demonstrators and against a repeat of a deadly crackdown against rallies in November sparked by a fuel price hike.

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"To the leaders of Iran - DO NOT KILL YOUR PROTESTERS," Trump tweeted in his occasional all-capitals style.

US Defence Secretary Mark Esper however said Trump was still willing to "sit down and discuss without precondition a new way forward" with Iran, but Tehran has steadfastly refused to hold talks with Washington unless it lifts sanctions first.

Iran's Supreme Leader Ayatollah Ali Khamenei (right) meets the Emir of Qatar Sheikh Tamim Bin Hamad Al Thani (centre) in the presence of President Hasan Rouhani, in the Iranian capital Tehran on Sunday. AFP

Tehran said it was interested in easing tensions in the region amid a standoff with arch-enemy Washington, which on January 3 killed a revered Iranian general, Quds Force chief Qasem Soleimani, in a Baghdad drone strike.

‘A critical time’

In a meeting between Iran's President Hassan Rouhani and the visiting emir of Qatar, both sides agreed de-escalation is the "only solution" to the regional crisis, the Qatari ruler said.

Iran's president also met with visiting Pakistani Foreign Minister Shah Mehmood Qureshi, whose country has offered to mediate between Tehran and US ally Riyadh.

Pakistan's Foreign Minister Shah Mahmood Qureshi (second left) meets Hassan Rouhani (right) in Tehran. AFP

In a meeting Sunday with Saudi Crown Prince Mohammed Bin Salman, Japanese Prime Minister Shinzo Abe warned military conflict with Iran will have an impact on global peace and stability, Japanese foreign ministry spokesman Masato Ohtaka said.

In a briefing to parliament, Hossein Salami, commander of Iran's Revolutionary Guards, said the missiles it fired last Wednesday on Iraqi bases hosting US troops were not aimed at killing American personnel.

The US said no American personnel were harmed in the attacks.

Mohammed Bin Salman (centre left) meeting with Shinzo Abe in the town of Al Ula, Saudi Arabia. AFP

Across the border in Iraq, the military said rockets slammed on Sunday into Al-Balad, an Iraqi airbase where US forces have been stationed, wounding two Iraqi officers and two airmen.

The base had held a small US Air Force contingent as well as American contractors, but a majority of these personnel had already been evacuated due to the tensions between the US and Iran, military sources told AFP.

Reacting to the latest attack, US Secretary of State Mike Pompeo tweeted: "Outraged by reports of another rocket attack on an Iraqi airbase.

An Iraqi army soldier stands guard near a US- made Iraqi Air Force F-16 fighter jet at the Balad Air Base, Iraq. File photo/AP

"These continued violations of Iraq's sovereignty by groups not loyal to the Iraqi government must end," he added.

There was no immediate claim of responsibility for Sunday's rocket attacks. The US has previously blamed such attacks on Iran-backed groups in Iraq.