Turkey's Prime Minister Recep Tayyip Erdogan says a Turkish air force jet has gone down over Syrian waters.

However, the prime minister told reporters in Ankara on Friday he could not confirm media reports that Syria shot down the plane. He said Turkish and Syrian vessels were searching for the plane and the pilots.

Erdogan held the press conference upon returning to Turkey from a visit to Mexico and Brazil.

Turkish media and Hezbollah's al-Manar television in Lebanon had reported that Syrian forces shot down the plane.

Reports say the plane incident triggered an emergency summit of Turkish military, intelligence and government officials.

Meanwhile, U.N. 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 U.N. special envoy's comments came after Syrian activists said 26 men reported to be pro-government “shabiha” militia fighters were killed in an ambush in the northern Aleppo province.

Rami Abdelrahman, the head of the Britain-based Syrian Observatory for Human Rights, told VOA on Friday that he received a video showing the bloodied bodies of the men piled on the side of a road.

“Over 26 people following the Syrian regime were killed west of Aleppo… this morning the people there said these people are from shabiha. We cannot confirm this, but we have received a video with over 26 bodies.”

In an apparent reference to the same incident, Syrian state media reported Friday that at least 25 people were killed by “armed terrorists” in the same region outside Aleppo.

The Observatory said it could not confirm whether the victims were civilians, as Syrian state media reported, or shabiha militants, who have been blamed for a series of deadly attacks on civilians in recent months.

The group also 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 International Committee of the Red Cross aborted its attempt to evacuate civilians from Homs Thursday after encountering close gunfire. The ICRC said it will attempt to go back to the area as soon as conditions permit.

The United Nations 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.

SOUNDBITE: Turkey's Prime Minister Recep Tayyip Erdogan (in Turkish)

Reuters: “We have no word on the pilots, but Turkish helicopters as well as four assault boats are searching for the pilots along with Syrian ships. We will see the outcome of this joint search operation.''

SOUNDBITE: Turkey's Prime Minister Recep Tayyip Erdogan (in Turkish)

APTN “Regarding the loss of our plane, I cannot say it was downed, without definite information. It is not possible to say that. But soon, we will have a (security) meeting in Prime Minister's Office. ”

SOUNDBITE: Erdogan (in Turkish)

APTN “The incident supposedly happened south of Hatay, 13 kilometres away from Latakia. Regarding our pilots, we do not have any information, but at the moment four of our gunboats and some Syrian gunboats are carrying out a joint search there (for the pilots). And we will see what kind of results this search will give us.”