Potential trading partners can rest easy about the investment environment in Iran despite sanctions pressure, the Iranian economics minister said Tuesday.

Some of Iran's trading partners have shied away from doing business with the Islamic republic because of sanctions targeting an economy that depends heavily on oil and gas revenues. Iranian Minister of Economic Affairs and Finance Ali Tayyebnia said from Tehran there should be no apprehension about trading with Iran.

"Iran is among the safest countries for (foreign) investment," he said.

Iran under the terms of a November 2013 agreement with six world powers working to resolve the nuclear impasse can export around 1 million barrels of oil per day. Monday's announcement that negotiators couldn't broker a comprehensive agreement left a question mark over Iran's energy-dependent economy.

Sanctions relief for Iran has been less valuable than expected, according to analysis from Bloomberg News. It found Iran brought in $2 billion less in cash and non-oil exports in the first six months of the year than anticipated by White House officials.

For oil products, Iran earned $5.6 billion more than it had year-on-year, but that money is isolated from Iran because of U.S. sanctions.

Iranian officials said Monday from Vienna some of the frozen funds may be released on a monthly basis as part of an extended relief package.

Iranian President Hassan Rouhani said Monday continued sanctions pressure against Iran would not "yield any fruit" for its nuclear negotiating partners. Russia, an Iranian economic ally and party to multilateral nuclear talks, has said it would work unilaterally to expand its trade relationship with Iran.

Iran said it plans to roll out new terms for oil contracts in the country during a February investment conference in London.

The new contract proposal would do away with buy-back contracts, where Tehran agrees to pre-set price, and replace them with a joint venture system, where international companies would be paid with a share of the output.