One photograph showed what a U.S. intelligence official described as a senior North Korean nuclear expert standing beside a key Syrian atomic official inside Syria.
Senior U.S. intelligence officials said the suspected reactor closely resembled the Yongbyon nuclear facility in North Korea, which tested a nuclear device in October 2006.
The U.S. charges come several months after North Korea missed a December 31 deadline to make a declaration of its nuclear programs in a deal over its nuclear ambitions with the United States, Russia, China, Japan, and South Korea.
Under the deal North Korea promised to disclose all of its nuclear programs and, ultimately, to abandon them and any nuclear weapons it may have.
"We hope that the fact that we have had such detailed understanding of this activity ... will convince them that there is no point in trying to cover up not only proliferation activity but (uranium) enrichment activity and plutonium activity," a senior U.S. official told reporters.
The United States hopes airing its suspicions about Syria will garner more international support to isolate Iran, which Washington accuses of seeking to develop nuclear weapons. Iran says its nuclear program is designed to produce electricity.
"One of our concerns is, is there (an Iranian) connection with North Korea? If there is, we don't know it," said a senior U.S intelligence official. "But is there something going on there that resembles this program that we are talking about in Syria - in Iran. That's a very large concern of ours."
Another official said Washington hopes the disclosures will persuade other nations "to join us in pressuring Syria to change its policies" toward Iraq, Lebanon and Palestinian groups that have launched attacks on Israel.
The United States accuses Syria of allowing insurgents to cross its borders into Iraq and of continuing to interfere in Lebanon despite the end of its military occupation.
It was not clear what effect the disclosures would have on North Korea, which was told about the presentations in advance. Nor was it clear whether they would ease concerns in Congress that the United States may have struck a bad bargain with North Korea.
U.S. President George W. Bush has lost the support of some fellow Republicans on the North Korea deal, but the Democrats who control Congress by and large appear to be more supportive of the path he is following.
Rep. Peter Hoekstra, the top Republican on the House of Representatives Intelligence Committee, said after a briefing on the issue that the administration had lost the trust of many lawmakers.
"This administration has no credibility on North Korea," he told Reuters. "A lot of us are beginning to become concerned that the administration is moving away from getting a solid policy solution to 'let's make a deal' - regardless of how bad it may be."
