CAIRO — Turkey’s president said Saturday that his country would do “whatever is necessary” in response to the downing of a Turkish military jet by Syria, adding a new complication to the tense relationship between the former allies split by Turkey’s support for Syrian rebels trying to overthrow the government.

“It is not possible to cover over a thing like this,” said President Abdullah Gul of Turkey, according to the Anatolia news agency. “Whatever is necessary will no doubt be done.”
Syria said Friday that its military forces had shot down a Turkish jet that had entered its airspace just off the Syrian coast. But Mr. Gul said Saturday that while the exact route of the plane had not yet been confirmed, it was routine for military jets flying at high speeds to briefly cross into another country’s airspace, and that the jet’s presence over Syrian territory was not intended as a hostile act.
The plane went down over the Mediterranean off the coast of the Syrian province of Latakia and south of the Turkish province of Hatay. On Saturday, Turkish officials confirmed that parts of the jet had been recovered.
Mr. Gul said the two governments were communicating at a high level despite the absence of a Turkish ambassador in Syria since Turkey closed its embassy in March. Syria’s state news agency, SANA, reported that the Syrian and Turkish Navies had established contact and were searching for the missing pilots.
Syria appeared eager to try to defuse the crisis. “We have no hostile intentions against Turkey,” Jihad Makdessi, a spokesman for the Syrian Foreign Ministry, told the Lebanese broadcaster LBC.
But Mr. Gul’s promise of retaliation — he did not specify whether he meant diplomatic or military measures — signaled Turkey’s anger. Faruk Celik, Turkey’s labor and social security minister, said that even if Syria’s airspace had been violated, the Syrian response was unacceptable, according to The Associated Press. “Turkey cannot endure it in silence,” Mr. Celik said.
Other Turkish officials urged restraint. Deputy Prime Minister Bulent Arinc said Turkey was awaiting an explanation from Syria about the downing of the plane, which he said was an unarmed surveillance craft. He called for calm while the details were sorted out, saying, “We should not give any credit to provocative acts and statements.”
The episode was another blow to relations between the neighbors, who were close before President Bashar al-Assad of Syria began his crackdown on Arab Spring protests 16 months ago, setting off a revolt by political and militia groups now supported by Turkey.
Turkey’s prime minister, Recep Tayyip Erdogan, has been one of the most strident critics of Mr. Assad’s government and its long crackdown, which has killed thousands since it began in March 2011.
Since then, Turkey has allowed more than 32,000 refugees to seek shelter in a string of camps across its 550-mile border with Syria. It has also provided crucial support to dissident groups and the Free Syrian Army, an anti-Assad militia whose leaders live under the protection of Turkish security forces in a fortified camp near the Syrian border.
On Friday, opposition activists reported that as many as 25 men had been shot dead in the village of Daret Azzeh, in northern Aleppo Province, in what the activists described as a battle between the Free Syrian Army and members of a pro-Assad paramilitary group.
On Saturday, Al Dunya television, a channel close to the Syrian government, dismissed those claims, saying those killed by the rebels were civilians and not armed fighters.
Opposition activists said the bloodshed continued on Saturday in cities and towns across Syria, with at least eight people killed. Shelling continued in the central city of Homs, where activists said at least one person was shot to death in the Khaldiyeh neighborhood and two others were killed in the rural suburb of Qusair.
An activist from the Revolutionary Council in Homs estimated that the shelling had wounded 400 people in the city, many of them seriously. He said that essential services had been cut off in the city. Syria’s restrictions on journalists make it impossible to confirm such reports.
Abou Bilal al-Homssi, an opposition activist in Homs, said that shelling had deterred the Red Cross from entering the area. “This is our second week under siege; the humanitarian situation is extremely dangerous,” he said.
In Deir al-Zour, near the border with Iraq, at least 28 people were killed on Saturday as Syria’s army battled rebels and shelled neighborhoods there, opposition activists told Reuters. The victims included women and children, according to hospital officials.
In the Tareeq Halab neighborhood of Hama on Saturday, security forces arrested young men and shelled the area, damaging the mosque of Fatima al-Zahraa, a local landmark, said activists with the Local Coordination Committees. The London-based Syrian Observatory for Human Rights, an opposition group with contacts in Syria, said that government forces killed at least two people in Hama on Saturday.
The Syrian Observatory also reported that the Syrian Army on Saturday raided the southern town of Dara’a, where the uprising against Mr. Assad was born, with tanks, killing one person. On Saturday, Mr. Assad announced the formation of a new cabinet, led by a longtime insider, Riad al-Hijab, according to state news media. But the move fell short of a pledge he made last month for a more inclusive government, as crucial ministers kept their positions, including Defense Minister Dawood Rajiha, Interior Minister Mohamed Ibrahim al-Shaar and Foreign Minister Walid al-Moallem.
Dalal Mawad and Hwaida Saad contributed reporting from Beirut, Lebanon, and Sebnem Arsu from Istanbul.