Iran sent new signals on Tuesday that it was seeking to subvert the Western sanctions on its contentious nuclear energy program, adding uncertainties in advance of another round of negotiations next week in New York before the United Nations General Assembly.

The Iranians said they had been engaged in talks with Russia, a member of the group of big powers negotiating with Tehran, about economic cooperation in energy, which could undercut the sanctions. South Africa, a former Iranian oil customer that has honored the sanctions in deference to Western pressure, said that, after talks with an Iranian delegation, it hoped to resume imports in three months.

On Monday, Iran’s negotiator at the nuclear talks, Abbas Araghchi, the deputy foreign minister, said his country would not countenance any new economic penalties imposed by the United States, after an announcement by the Obama administration last month that it was adding more than 25 Iranian individuals and companies to a sanctions blacklist.

The atmosphere contrasts starkly with President Hassan Rouhani’s first visit to the United Nations last September for the General Assembly’s annual convergence of world leaders. The Iranian president spoke optimistically of a new era and prospects for a nuclear deal — capped by a groundbreaking telephone conversation with President Obama.