US President George W Bush has promised extra help to tackle Kurdish rebels in northern Iraq, following talks with Turkish PM Recep Tayyip Erdogan.
Mr Erdogan and Mr Bush spoke of closer ties between their countries
Mr Bush offered to share intelligence with Turkey and declared the PKK rebel organisation "an enemy of Turkey, a free Iraq and the United States".
Turkey has threatened to hit bases used by the PKK (Kurdistan Workers' Party) unless the US and Iraq do more to help.
Washington has urged Ankara not to launch cross-border strikes into Iraq.
US officials fear such action could destabilise northern Iraq, up to now the most stable region of the country.
The Turkish government is under public pressure to use force against the PKK following a series of deadly attacks in Turkey, and has sent thousands of troops to the Iraqi border.
Speaking in Washington at a joint news conference with Mr Erdogan, Mr Bush pledged to strengthen political and military cooperation and to improve intelligence sharing between the US, Turkey and Iraq.
"I made it very clear to the prime minister that we want to work in a close way to deal with this problem," Mr Bush said.
"We talked about the need to have better intelligence sharing.
"In order to chase down people who murder people, you need good intelligence. We talked about the need for our militaries to stay in constant contact."
Mr Erdogan said Ankara saw it as very important that there was a unified approach to tackling the PKK rebels.
Kurdish demonstrators protested outside the White House
"As strategic partners we are fighting jointly against terrorism in the world," he said.
He warned that the stability of the whole region would be affected by what happened in northern Iraq.
Before leaving for Washington, Mr Erdogan said the meeting came at a critical time for US-Turkish relations and expressed hope that the talks would produce "concrete measures".
Kurdish protesters demonstrated outside the White House on Monday, voicing their opposition to any violent action by Turkey.
The Kurdish rebels have intensified their campaign during the past month, killing at least 40 people, military and civilians, in Turkey.
The PKK has waged a violent campaign for a Kurdish homeland since 1984, resulting in more than 30,000 deaths.