BAGHDAD – The United States followed through Friday on its promise to release nine Iranians held in Iraq, including two accused of helping smuggle weapons into Iraq.

The release wasn’t without surprise, however. One of the captives had been in U.S. custody nearly three years, and at least four were picked up in military actions directed against Sunni insurgents and not the Shiite militias that Iran is suspected of assisting.

U.S. officials said they were still holding 11 Iranians, but the Iranian ambassador to Iraq insisted that the number still held was 25, and he demanded that Iraq continue to press for their release.

“Since these diplomats were kidnapped by U.S. forces on Iraq’s soil while performing their diplomatic duties and they enjoyed diplomatic immunity, the Iraqi government is obliged to do its best to hasten their release from illegal arrest,” Ambassador Hassan Kazemi-Qomi said.

The nine were surrendered to Iraqi authorities, who then turned them over to Iranian officials.

The U.S. military took pains to characterize the releases as routine, noting that an average of 50 captives are freed daily.

A senior U.S. military official, while cautioning that the Iranian government shouldn’t see the releases as a sign of improving relations, said he hoped they would encourage Iran to stick to its vow not to supply weapons to militias.