The latest talks between Iran and the five permanent members of the U.N. Security Council -- the United States, Britain, France, Russia and China -- along with Germany ended this week Moscow with few developments.
Members are at odds over the purity level at which Iran is enriching uranium. Tehran maintains it has a right to peaceful enrichment, though its critics say the program is progressing toward the level needed to make a nuclear weapon.
"The secretary-general appeals to the parties to resume their diplomatic engagement with renewed intensity and with the utmost flexibility," the statement read.
Iran, meanwhile, announced the arrest of 20 people it said were involved in the assassination of Iranian nuclear experts. Intelligence officials said they were rounded up in a series of sting operations conducted across the country, Iran's state-funded broadcaster Press TV reports.
Iran added this week that it believed its Western adversaries were behind malware attacks on its energy and nuclear industries.