What's at stake for business in Iran's nuclear deal

If the Iran nuclear deal fails then all the countries involved have a lot to lose -- and not just for political and security reasons.

If US President Donald Trump, as expected, refuses to certify to Congress that Iran is complying with the deal, that could pave the way for future sanctions, which could have a big impact on countries and companies that have re-engaged with Tehran since the 2015 deal.

The nuclear agreement is designed to prevent Iran developing a nuclear weapon, and saw Tehran halt its nuclear programme in exchange for the lifting of international sanctions.

Since it came into force in January 2016, the Iranian market of 80 million people has been opened up to European, Russian and Chinese businesses.

Many investors have held back but others, including several large companies, have already concluded some big deals, including European aircraft manufacturer Airbus which has signed agreements with Iran to deliver 100 aircraft.

Here are some of the other major trading partners and what's at stake for them:

Before sanctions, Germany was Iran's main trading partner.

After the lifting of sanctions, German exports to Iran increased by 26 percent in 2016, and continue to rise, according to the federation of German industry (BDI).

The Siemens group relaunched in Iran in March 2016, signing an energy agreement with Iranian power and infrastructure group Mapna.

Daimler signed letters of intent with two Iranian groups in January 2016 to produce and market Mercedes-Benz trucks.

"Companies that have since resumed commercial relations with Iran and are also active in the United States would be extremely destabilized by the reintroduction of sanctions," warned the BDI.

Trade, which had collapsed under sanctions, rebounded dramatically after the end of sanctions, rising by 235% in 2016, mainly due to oil imports.

Carmaker Peugeot-Citroen (PSA), which was forced to leave Iran in 2012, returned in 2016 after signing production deals worth 700 million euros.

Renault, which had remained in the country and already makes about 200,000 cars per year there, signed a joint venture agreement to step up production and make more than 300,000 cars a year.

Total, for its part, was the first Western oil group to return to Iran in more than a decade. It signed a $4.8 billion gas deal in early July, heading an international consortium alongside Chinese CNPC.

Trade between the two countries, which had collapsed due to sanctions, saw a sharp rise in 2016, to such a level that Italy was named the first trade partner of Iran in the EU.

In 2016, Rome and Tehran signed a number of agreements, including in tourism, renewable energy and railways.