Germany has banned Iran's Mahan Air from landing in the country with immediate effect, citing security concerns and the airline's involvement in Syria.

Mahan Air is on a United States sanctions list and Washington has long urged allies to ban the airline from their territory.

The decision to ban the airline came after consultations with European allies and the US, Chancellor Angela Merkel's spokesman Steffen Seibert told reporters.

"It cannot be ruled out that this airline carries out transports to Germany that affect our security concerns," said Seibert.

"This is especially true against the backdrop of terrorist activities, intelligence on terrorist activities from the Iranian side and Iranian entities in Europe in the past."

US Secretary of State Mike Pompeo welcomed the German decision.

"The airline transports weapons and fighters across the Middle East, supporting the Iranian regime's destructive ambitions around the region," he said in a tweet. "We encourage all our allies to follow suit."

Mahan, Iran's second-largest carrier after Iran Air, flies four services a week between Tehran and the German cities of Duesseldorf and Munich.

The move comes at a time of sensitive relations with Iran. Germany plays a large role in trying to salvage the 2015 nuclear deal with Tehran after US President Donald Trump's decision to unilaterally pull out of it last year.

Why is Mahan Air allowed to fly into Munich and Düsseldorf? I’m going to keep asking everyday. Read the fact sheet on them for yourself. https://t.co/Bvo16nvupo — Richard Grenell (@RichardGrenell) 14 settembre 2018

German firms have come under intense pressure from the US to halt their business with Iran. As a result, rail operator Deutsche Bahn, telecom company Deutsche Telekom, Mercedes-Benz parent Daimler and industrial group Siemens have said they will stop their operations in the country.

The European Union earlier this month targeted sanctions at Iran's security services and two of its leaders, accused of involvement in a series of murders and planned attacks against Tehran critics in the Netherlands, Denmark and France.

The mounting pressure over Iran is increasing following President Trump's decision last year to pull Washington out of the nuclear non-proliferation treaty it had reached with Tehran under his predecessor Barack Obama.