A scientific-cooperation pact between North Korea and Iran could advance the nuclear and missile programs of both countries. The U.S. is paying new attention to the pact after recent North Korean nuclear and missile tests, at a time when Tehran has come closer to producing enough enriched nuclear fuel for a bomb.

U.S. and European officials are particularly concerned about the presence at the Tehran signing of the head of the Atomic Energy Organization of Iran, Fereydoun Abbasi-Davani. The U.N. placed sanctions and a travel ban on Mr. Abbasi-Davani in 2007, on what it said was evidence he was involved in nuclear-weapons research.

Iranian state media reports don't specify cooperation with North Korea on developing nuclear technologies. But they do cite the establishment of joint laboratories, exchanges of Iranian and North Korean scientists, and technology transfers in the areas of energy and information technology.