Russia has to postpone the delivery of Sukhoi Su-35 multirole fighter jets to Indonesia due to complications caused by U.S. sanctions, Russian newspaper Kommersant reported on Thursday, October 4, citing two top managers from Russian defense industry enterprises and a source close to the government.

The Russia-Indonesia deal for 11 Su-35s has reportedly retained its legal force, but its implementation will be postponed. One of the newspaper’s sources called the situation “unpleasant,” but “not critical.”

Negotiations for the contract began in November 2015 but were held up over countertrade deals and offset obligations. The $1.1 billion agreement was finally signed in February, and Indonesia was expecting to receive the first two aircraft by October.

According to Kommersant, Russia fears the introduction of the U.S. sanctions against a commercial bank, which was supposed to participate in the implementation of the contract. At the same time, U.S. authorities did not provide Indonesia with guarantees that they would not impose sanctions for cooperating with the Russian defense industry.

The Su-35 is a multirole 4th generation super-maneuverable thrust-vectoring fighter jet equipped with a phased array radar. The aircraft’s top speed is reportedly 2,500 km/h (1,500 mph) and it has a combat radius of around 1,600 km (1,000 miles). It carries a 30mm gun and has 12 external hardpoints.