Closing out a weeklong trip to the Middle East, including a visit to Iraq, the Republican presidential hopeful said he was concerned about a large supply of explosives found in Iraq, hinting they may have come from Iran, CNN reported.

During a press conference in Amman, McCain said concern still exists that Iran could be training Iraqi extremists in Iran then returning them to Iraq.

McCain, the presumptive GOP presidential nominee, said he was worried about Iran developing nuclear weapons. If elected president, McCain said he would work with allies in Europe to implement a strict set of sanctions "that would be harmful and compelling" to Iran's trade, diplomatic and financial institutions.

"There'd be a broad range of sanctions and punishments to the Iranians to help try to convince them that their activities -- particularly development of nuclear weapons -- is not a beneficial goal to seek," he said.

Progress he saw in Iraq as well as his meeting with King Abdullah II' title='King Abdullah II' class='tpstyle'>King Abdullah II of Jordan were encouraging, McCain said.