Turkey has promised to take the “necessary steps” in response to Syria's admission that it downed a Turkish air force jet that had flown into Syrian airspace.

Turkish Prime Minister Recep Tayyip Erdogan issued a statement after an emergency security meeting in Ankara, saying a decisive response will be taken once all the facts about the incident are known.

Syrian officials said the low-flying warplane was shot down over the Mediterranean Sea Friday.

Syrian forces are helping the Turks search for the two missing Turkish pilots.

Turkey has joined nations such as the United States in saying that Syrian President Bashar al-Assad should step down because of the uprising in his country.

The United Nations envoy for Syria, Kofi Annan, told reporters in Geneva Friday that “countries of influence” need to persuade both sides in Syria to “stop the killing and start the talking.” He said it is time for countries to “raise the level of pressure” on both Syria's government and the opposition to end violence in the country.

Mr. Annan said Iran should be “part of the solution” for bringing peace to Syria. Russia has pushed for Iran's involvement in resolving the conflict, while the U.S. has said Iran should not be involved.

The Britain-based Syrian Observatory for Human Rights reported fresh clashes Friday between government troops and rebels in the flashpoint city of Homs, where hundreds of civilians are believed to be trapped and unable to find shelter.

The U.N. says up to 1.5 million Syrians are now in need of humanitarian assistance as it warns of a deteriorating situation in Syria. The figure reported by the U.N. Office for the Coordination of Humanitarian Affairs is up from an earlier estimate of 1 million.