ISTANBUL, Dec. 6 (Xinhua) -- Turkish Prime Minister Recep Tayyip Erdogan on Sunday ruled out sending more troops to Afghanistan as requested by the United States before heading for Washington.

    Erdogan said that Turkey has already contributed the "necessary number" of troops. However, it is willing to train the Afghan army and police. The 1,700 Turkish troops in Afghanistan are involved in patrolling the capital city of Kabul instead of combat missions.

    The Turkish prime minister made the statement at Istanbul's Ataturk Airport prior to his visit to the United States.

    On Monday, he will meet with U.S. President Barack Obama, who announced last Tuesday the deployment of 30,000 more U.S. soldiers to Afghanistan.

    The topic of sending additional troops to Afghanistan is expected to be on the agenda in the meeting between the two leaders.

    The United States has appealed to its allies for reinforcements in the conflict in Afghanistan and it hopes Turkey to play a bigger role in the war against the Taliban and al-Qaida.

    Erdogan said Turkey has invested 150 million U.S. dollars in Afghanistan in the fields of education, health and infrastructure and additional 50 million dollars would be invested in the first phase.

    "All these are sincere steps have been taken to carry our historical association and brotherhood into the future and we will carry on taking these steps," he said.