Tehran ? Defying week-old U.N. sanctions over its nuclear program, Iran promised to expand its atomic research Wednesday as its president vowed to punish the West and force it to “sit at the negotiating table like a polite child” before agreeing to further talks.

Tehran, which insists its nuclear work is peaceful, said it will build four new reactors for atomic medical research. The U.S. and some of its allies believe Iran is trying to develop nuclear weapons, and the Islamic Republic’s plans to expand research could encourage calls in the West for more economic pressure against the country.

President Mahmoud Ahmadinejad said Iran will not make “one iota of concessions.”

The Obama administration took its first step in implementing new sanctions Wednesday, leveling penalties against additional individuals and institutions it says are helping Iran develop its nuclear and missile programs and evade international sanctions.