WASHINGTON (AP) - About a dozen U.S. fighter jets will be flying and conducting training operations in Jordan, poised to respond if needed to protect allies if the war in neighboring Syria spills over the border, U.S. administration officials said Friday. The increased show of U.S. military might - which brings the total number of U.S. forces in Jordan to as many as 1,000 - should be seen as a signal to Syria that it must confine its 2-year-old civil war within its borders, officials said. The officials said it is meant to show that the U.S. is committed to its defense relationship with Jordan and that America intends to maintain a strong presence in the region. The officials added, however, that the decision to keep the F-16 fighters there is not a first step toward establishing a no-fly zone around any parts of Syria and should not be interpreted as a move to begin staging American troops there for possible military action in Syria. The officials spoke on condition of anonymity because they were not authorized to discuss the mission publicly. The F-16 fighters, along with a Patriot missile battery and about 700 U.S. troops, are staying in Jordan beyond an international military exercise, which ended this week. The decision significantly increases the number of U.S. troops in Jordan, adding to the approximately 250 that have been there for some time. Jordan had asked the U.S. to leave some military troops and equipment behind. Defense Secretary Chuck Hagel approved the order last week for the U.S. Air Force to leave the fighters there, and military officials have been working to carve out exactly what the troops' mission will be in the coming weeks and months. No date has been set for the forces to leave. In a letter to congressional leaders, President Barack Obama said Friday, "the detachment will remain in Jordan, in full coordination with the government of Jordan, until the security situation becomes such that it is no longer needed." The training mission also provides a way for the fighter pilots to meet their flight requirements. F-16 pilots are required to fly nine or 10 sorties a months in order to remain combat ready. The added U.S. military support to Jordan comes as the Obama administration hammers out details to provide lethal aid for Syrian rebels. U.S. officials announced earlier this month that they had conclusive evidence that Syrian President Bashar Assad's regime has used chemical weapons, including the nerve agent sarin, on a small scale against opposition forces. As a result, officials said that Obama authorized sending weapons to Syrian opposition groups - a policy shift after months of wrangling over whether or not the chemical weapons had actually been used. Obama had said that the use of chemical weapons would cross a "red line" triggering greater U.S. involvement in the civil war. Syrian rebels have been pressing for additional weapons, including anti-tank and anti-aircraft missiles, but administration officials have worried that high-powered weapons could end up in the hands of terrorist groups. Officials have said that the CIA would largely coordinate the delivery of arms to the rebels. The CIA has led U.S. outreach to the rebels from outside Syria, meeting them at refugee camps and towns along the Turkish and Jordanian borders. The U.S. troops were in Jordan for a 12-day military exercise, dubbed Eager Lion, which ended this week. It included land, air and sea maneuvers across the country and involved about personnel from 19 Arab and European nations. Associated Press writer Julie Pace contributed to this report.