BERLIN, Aug 12 (Reuters) -

German exports to Iran fell by nearly half in the first six months of 2019, data showed on Monday, suggesting companies are scaling back business ties with Tehran to avoid trouble with the United States after Washington reimposed sanctions.

Sales to Iran plunged by 48% to 678 million euros ($758.8 million) from January through June year-on-year, data from the Federal Statistics Office reviewed by Reuters showed. Imports from Iran declined by 43% to nearly 110 million euros.

"The fact that trade between Iran and Germany has collapsed that massively is not a big surprise, unfortunately," the BGA trade association said.

It pointed to the extra-territorial character of recent U.S. sanctions which means that companies from third countries are also punished if they do business with Iran.

"German companies are forced to choose between their market activities in Iran and the United States, so it's clear which market is preferred," BGA said.

President Donald Trump last year pulled the United States out of a nuclear accord between Iran and major powers. Under the 2015 deal, international sanctions against Iran were relaxed in exchange for Tehran curbing its nuclear programme.

Despite the U.S. decision to reimpose the sanctions, Germany, France and Britain are trying to rescue the agreement by setting up a barter-based trade conduit with Iran, but an Iranian mirror mechanism has yet to be established.

If the mechanism, also know as Instex, goes ahead, it would initially deal only in products such as pharmaceuticals and foods, which are not subject to U.S. sanctions.

Iranian officials have repeatedly said Instex must cover oil sales or provide substantial credit facilities for it to be beneficial.

Last year, Germany exported mainly machinery, chemical products and cars and car parts to Iran.