The sources told AFP that envoys from the 28 member states of the European Union approved the decision in principle, which will now go to ministers for formal approval, possibly on Friday.
The sanctions were due to expire at the end of July and will now run to January 2017, they said.
The sanctions target the oil, financial and defence sectors of the Russian economy and were first imposed after the shooting down of Malaysia Airlines flight MH17 in July 2014, blamed on pro-Moscow rebels in eastern Ukraine.
The EU last week rolled over for another year to June 2017 separate sanctions imposed after Russia’s March 2014 annexation of Crimea from Ukraine.
The EU has also imposed a separate set of visa ban and asset freeze measures against individual Russian and Ukrainian figures for backing the separatist cause in early 2014. These measures run until September.