Attending the meeting will be US Secretary of State Hillary Clinton, plus foreign ministers from France, Germany and Poland, and representatives from NATO and the United Nations.
Turkey's President Abdullah Gul will host a trilateral meeting with Pakistan's President Asif Zardari and Afghanistan's Hamid Karzai on Tuesday.
The Afghan government and its foreign backers are preparing for the end of 2014, the deadline for foreign combat troops to return home, even though some foreign troops will remain as trainers and advisers.
Some Afghans fear their own security forces will be unable to cope with the insurgency when the majority of foreign troops go and that their country may fall into another civil war.
Wednesday's Turkish session with the Afghan and Pakistani leaders is meant to agree on a framework for regional security and cooperation. This will include Afghan border nations Pakistan, Iran, China, Turkmenistan, Tajikistan and Uzbekistan, ahead of a wider-ranging meeting in Germany in December.