Joseph Ralston, a retired US air force general, held talks with Turkish leaders and said that Washington understood the need to stop the actions of the Kurdistan Workers Party (PKK).
At a news conference with Turkish foreign ministry officials on Wednesday, Ralston said: "We need them [measures] urgently and they need to be visible so that not only the Turkish public, but the Iraqi public and the American public can see that we are serious about eliminating the threat of terrorism."
The appointment of the former Nato supreme allied commander and former US deputy chief-of-staff is meant to show Washington's commitment to helping Turkey and Iraq confront the PKK, which the US lists as a terrorist organisation.
Turkey has repeatedly complained about what it says is a lack of US cooperation in the struggle against the group and has repeatedly signalled that it could take unilateral military action against the PKK in Iraq if necessary.
Edip Baser, a retired Turkish general, has been appointed to work with Ralston and appealed for people to be patient.
"We hope that positive results will be achieved in a short time," he said.
Turkish officials were expected to ask Ralston for US military action - possibly with help from Iraqi forces - against senior PKK commanders, but the stretched US military is unlikely to pursue PKK fighters hiding in the remote mountains along the border shared by Iraq, Iran and Turkey.
In a television interview, Ralston said a military solution was always the last option.
Abdulkadir Aksu, the interior minister, said after meeting Ralston that he had asked that the PKK be prevented from getting arms and logistic support.
Aksu said: "There is a serious security vacuum. The terrorist organisation has access to arms sources which should be in the control of the Iraqi government. This has to be prevented."
Turkish intelligence reports have said that the PKK has had access to weapons belonging to the Iraqi military.
The PKK is estimated to have about 5,000 fighters operating in Turkey, Iraq and Iran.
Ten people died in an explosion in
predominantly Kurdish Diyarbakir
Meanwhile, police raided several houses in Diyarbakir after the bomb blast that killed at least 10 people on Tuesday.
No group said it carried out the explosion at a bus stop in the city in the mainly Kurdish southeast of the country.
The PKK condemned the bombing and said it was not responsible, blaming elements within the Turkish state instead.
A PKK statement carried by the Firat News Agency read: "This attack was carried out by some forces in the Turkish special war system in order to sabotage this [peace] process."
The Kurdistan Liberation Hawks (TAK), a group believed to be linked to the PKK and which claimed responsibility for attacks in August, has not commented. TAK has threatened to turn Turkey into "hell" over its policies towards the Kurds.
Police said they believed the device was set off by mistake and was intended for a police headquarters 1.5km away.