Moscow says it has urged Tehran to revoke a lawsuit previously filed over Russia’s failure to meet contractual commitments to deliver S-300 air defense systems to Iran.

A source in the Russian military technical cooperation establishment told TASS news agency that fresh talks were currently underway to supply S-300 missiles to Iran; however, differences over the timetable for revoking Iran’s lawsuit against Russia for not honoring the previous contract remain a bone of contention.

“Iran says it will revoke the lawsuit regarding the previous contract when it gets the first batch of products under the new contract, while Russia insists the lawsuit should be revoked before it takes any action under the newly-concluded deal,” the source said.

Under the 2007 contract, Moscow pledged to deliver to Iran five battalions of the S-300 air defense system, worth 800 million dollars.

Moscow, however, reneged on the agreement with Tehran in 2010 under the pretext that the agreement was covered by the fourth round of the UN Security Council sanctions against the country over its nuclear program. The resolution bars hi-tech weapons sales to the Islamic Republic.

On April 13, Russian President Vladimir Putin signed a presidential decree paving the way for the long-overdue delivery of the defense system to Iran.

The decision to deliver the systems came after Iran and the P5+1 group of countries – the United States, France, Britain, China and Russia plus Germany – reached a mutual understanding on the Islamic Republic’s nuclear program in the Swiss city of Lausanne on April 2. The two side later reached a comprehensive agreement.

Last month, Vladimir Kozhin, Putin’s aide on military and technical cooperation, said the S-300 system is to be modernized before being delivered to Iran.

Meanwhile, a large Iranian delegation is reportedly in Moscow to participate in the MAKS 2015 show, and hold talks on military-technical cooperation, including negotiations over S-300.