The U.N.'s International Atomic Energy Agency said satellite images of an Iranian nuclear facility and military site indicate that weapons research may be taking place there.
IAEA chief Yukiya Amano expressed concern last week over images of activities at the site, Reuters reported.
A U.S. security institute specializing in nuclear proliferation, said it now has satellite imagery that backs up the IAEA's concerns.
"The new activity seen in the satellite image occurred outside a building suspected to contain an explosive chamber used to carry out nuclear weapons related experiments," the Institute for Science and International Security, said on its website in a May 8 report.
Iran has repeatedly refused to allow the IAEA inside the Parchin plant, a point inspectors plan to raise at the second round of P5+1 talks in Baghdad on May 23. The P5+1 is made of the U.S., U.K., China, Russia, France and Germany.
Meanwhile, Prime Minister Benjamin Netanyahu and senior Israeli officials met with E.U. Foreign Policy chief Catherine Ashton Wednesday in Jerusalem. At the meeting, Netanyahu said "Iran is using these talks to play for time."
"There is no evidence whatsoever that the Iranian government has any intention to cease its aggressive pursuit of nuclear weapons," Netanyahu told Ashton during her one-day visit to Israel.
Defense Minister Ehud Barak, Foreign Minister Avigdor Lieberman and newly appointed Deputy Prime Minister Shaul Mofaz were among the senior officials who met with Ashton.
Israel said in order for diplomacy to succeed, Iran must agree to stop producing enriched uranium, get rid of its stockpile, and dismantle its uranium enrichment facility at Qoms, all of which it has repeatedly refused.