Syria's downing of a Turkish plane marks a serious escalation of the Syrian crisis, which risks spilling over into neighbouring countries, Iraq warned on Saturday as Turkish Prime Minister Tayyip Erdogan prepared for a second security meeting with top officials over the issue.

The meeting will be Erdogan's second security meeting over the incident in less than 24 hours and follows a separate meeting between Turkey's foreign minister and senior military commanders.

According to media reports, the Turkish and Syrian navies conducted a joint search on Saturday for the jet and the airmen shot down by Syria over the Mediterranean, only a short distance from a Turkish province hosting thousands of rebels fighting President Bashar al-Assad.

Signals from both sides suggested neither wanted a military confrontation over Friday's shooting down of the jet near their borders. However, the joint operation will clearly sit uneasily with both forces, given the bitter hostility between the two former allies over Assad's 16-month-old crackdown on opponents.

Earlier in the day, Turkish President Abdullah Gul said it was not possible to ignore the fact that Syria had shot down a Turkish fighter jet and said everything that needed to be done following the incident would be done, Turkish media reported.

'It is not possible to cover over a thing like this, whatever is necessary will be done,' Gul was quoted as saying by state news agency Anatolia. It was not immediately clear where he was speaking.

Gul said it was routine for jets travelling at high speed to cross borders for a short distance. He said an investigation into the incident would look at whether the plane was downed in Turkish airspace, media reported.

Gul also said Ankara had been in telephone contact with Damascus and that a search operation for the plane and missing pilots was still under way.

Iraq, which borders both countries, said the incident marked a serious escalation of the Syrian conflict and demonstrated its potential to infect other countries in the region.

'Our main concern is the spillover of the crisis into neighbouring countries,' Iraqi Foreign Minister Hoshiyar Zebari told a news conference with his Swedish, Bulgarian and Polish counterparts in Baghdad.

'No country is immune from this spillover because of the composition of the societies, the extensions, the connections, the sectarian, ethnic dimensions,' he said.

If the conflict were to slide into an all-out sectarian or civil war, Iraq, Lebanon, Jordan and Turkey would all be affected, he said. 'This is not an excuse to do nothing about Syria, no. But there will be an impact.'

He said the crisis had intensified in recent days with the shelling of civilian residential areas, increase in the number of demonstrators killed and the defection of a Syrian pilot who flew his plane to Jordan.

'The shooting down yesterday of a Turkish aircraft over Syrian territorial waters - this is a serious escalation and indication that the conflict would have (a) far bigger impact than (on) Syria itself,' Zebari said.

Zebari held talks with the three other foreign ministers who are on an EU-backed mission to help seek solutions to the Syria crisis.

The trio visited Lebanon on Friday and will report their findings to EU foreign ministers at a meeting in Luxembourg on Monday.

'Iraq is part of the region, Iraq is part of the solution. It is important that the countries that are the most affected, but also perhaps have the greatest possibility to influence developments in Syria, are fully part of the efforts,' Swedish Foreign Minister Carl Bildt told the news conference, adding that they were 'appalled' by what he said were human rights abuses in Syria.

Iraq's Shi'ite-led government has adopted a more moderate position on Syria than Sunni Gulf states Qatar and Saudi Arabia, which have advocated supplying arms to the Syrian rebels.

An Arab diplomat said on Saturday that Qatar and Saudi Arabia were paying salaries to rebel forces fighting in the Syrian revolt.

Bulgaria's Nickolay Mladenov said Iraq's transition after the fall of Saddam Hussein could be a model for Syria.

'Iraq itself went through a transformation from dictatorship to a democratic environment and in a lot of ways the opposition parties in Iraq came together, particularly in the north,' he told Reuters. Iraq shares its northwestern border with Syria.

Meanwhile, UN Secretary-General Ban Ki-moon said he hoped that Turkey and Syria will exercise restraint over the issue.

'The secretary-general is following the situation closely. He hopes this serious incident can be handled with restraint by both sides through diplomatic channels,' Ban's spokesman Martin Nesirky said in an emailed statement.

Turkey has so far been measured in its response to the incident although Erdogan's office has said Ankara will act 'decisively' but only when all the details are known.-Reuters