The U.S. military in Iraq says coalition forces have killed six suspects and detained 18 others in separate operations targeting al-Qaida in Iraq terrorists.

A military statement says 10 suspects were detained in Baghdad for their connection to a senior al-Qaida in Iraq commander, and seven were arrested in Taji.

In western al-Anbar province, six suspects were killed and one arrested in two separate raids on areas north of Fallujah.

Meanwhile, U.S. Defense Secretary Robert Gates said Thursday that the United States is looking to a long-term military presence in Iraq similar to its arrangement with South Korea.

Gates says the presence would be based on a mutual agreement with Iraq, which would protect the sovereignty of Iraq's government and limit what U.S. forces can do while in the country.

Earlier, the U.S. ground forces commander in Iraq said he may need more time to assess the impact of the U.S. troop surge in the country, beyond the September assessment President Bush and Congress are expecting.

Lieutenant General Ray Odierno said the last of the additional U.S. combat troops will not be in place until mid-June. He said they will need considerable time after that to make a major impact.

The general also said the U.S. military is increasing efforts to reach out to insurgent groups to get them to stop their attacks.