Medvedev said he had raised his concerns over the issue with EU leaders at a summit in Siberia last week, according to a transcript of the interview published on his official Internet site, www.kremlin.ru.
"If we are conducting negotiations with Iran … we should not take actions which incite the Iranian leadership and are aimed at the introduction of additional sanctions," he said in the interview to media outlets from Group of Eight countries before next week's G8 summit in Japan.
"For me it is completely unclear why such a decision was taken recently by the European Union," said Medvedev.
"I mean, either we talk to them (the Iranians) or we use every petty excuse there is to tweak our negotiating partners."
Western powers suspect Iran of using its civilian nuclear programme as a cover for bomb-making activities, but Tehran denies this.
Russia has supported United Nations efforts to persuade Iran to answer questions about its nuclear programme, but it has consistently watered down Western-backed sanctions, saying positive engagement is more effective than threats.
Late last month the EU agreed new punitive measures targeting businesses and individuals the West says are linked to Iran's nuclear and ballistic programmes. (Writing by Christian Lowe; Editing by Matthew Jones)
