Presidential hopefuls spar over economy as Trump turns screws on Iran

* Rivals say Rouhani waited in vain for foreign investment

* Nuclear deal overshadowed by low oil price

* Unemployment up despite lifting of sanctions,

* Trump's toughened stance creates uncertainty

By Bozorgmehr Sharafedin

LONDON, May 8 (Reuters) - President Hassan Rouhani's trip to the coal mine in northern Iran was all going to plan, until the crowd massed in front of his car chanting "it's a day of mourning for workers".

Seconds later, shaky footage of Sunday's protest showed a man jumping onto the bonnet and stamping hard on the metalwork, a rare direct confrontation against the background of a highly-charged election race that keeps returning to one subject - Iran's stuttering economy.

Rouhani was officially there to visit families bereaved by an explosion at Zemestanyurt mine last week. But the protest slogans broadened out into other areas - poor safety standards, late payments, poor insurance coverage and seasonal unemployment.

Media outlets supporting Rouhani's conservative rivals, who have repeatedly accused him of failing to deliver the jobs and growth he said would follow his landmark nuclear deal, posted the film far and wide on social media. "The devastated miners cannot live with Rouhani’s hollow promises," said Tasnim agency.

Other agencies, including ISNA, suggested the crowd in Golestan province had been infiltrated by Rouhani's enemies. The slogans were striking similar to ones shouted by protesters who disrupted the president's May 1 campaign speech at the mausoleum of the late Ayatollah Ruhollah Khomeini.

Staged or not, the slogans echoed the battle-cries of the broader election campaign, where Rouhani's rivals have focused on his handling of an economy threatened by high unemployment, low oil prices, slow growth outside the crude sector and a new, unpredictable foe in U.S. President Donald Trump.

"All the positive results of the nuclear deal and lifting of sanctions have been overshadowed by the low prices of oil," economist and Rouhani supporter Saeed Laylaz told Reuters in a phone interview from Tehran.

The 2015 deal that Iran signed with world powers to limit its nuclear work in exchange for lifted sanctions - a pact that Rouhani has held up as his signature achievement - provided a short-term economic boost.

Inflation dropped to single digits under his watch and real GDP grew by as much as 7.4 percent. But the economy, largely reliant on oil exports, took a hit when prices plunged from $104 to $44 per barrel.

OIL, UNEMPLOYMENT

Rouhani's rivals say the president bet too strongly on rapprochement with the West, waited in vain for foreign investment, and did too little at home to improve national production.