Thousands of protesters will greet President George Bush in Ireland today as he starts a diplomatic offensive to bridge deep transatlantic divisions over America's policy in Iraq.

Thousands of protesters will greet President George Bush in Ireland today as he starts a diplomatic offensive to bridge deep transatlantic divisions over America's policy in Iraq.

Mr Bush will spend 18 hours in the west of Ireland attending a three-hour-long, pre-scripted meeting with EU leaders and officials today. Tonight he leaves for Istanbul where Monday's Nato summit will be held. It is expected to be dominated by the issue of Iraq.

Just days before the handover of power to the interim government in Iraq, Mr Bush's visit comes at an acutely sensitive time, with leaders on both sides of the Atlantic anxious to avoid more public rifts. The depth of the divisions caused by Mr Bush's Iraq policy is clearly illustrated, however, by the extraordinary security operation in Ireland, and the coolness of the reception from a nation that prides itself on its links with the US.

About 4,000 police and 2,000 soldiers ­ more than a third of Ireland's security force ­ are deployed around Dromoland Castle, a luxury hotel in Co Clare that is hosting today's summit. In addition, 700 US security personnel and four naval ships are being called in.

Activists have planned protests both in Dublin and at the summit venue close to Shannon airport, itself a strategic refuelling point used by US military planes en route to Iraq.

However, Ireland's alert will be dwarfed by the security operation in Istanbul, where Turkish police are expected to deploy more than 23,000 officers for the Nato leaders' summit. Alarmed by Thursday's bomb attack, which killed four people, security forces were yesterday already closing off streets in the area that will play host to President Bush and the leaders of 45 other countries which are either in Nato or have a partnership with it.

A vehicle full of explosives was found at Istanbul's international airport last night, a local television station, CNN Turk, reported. An airport official said investigators had so far found no evidence of a bomb.

Topics at today's summit with the EU include Iraq counter-terrorism, trade, a global satellite navigation system, efforts to curb the spread of nuclear weapons as well as policy towards the Middle East. EU officials hope that, on what is probably his last visit to Europe before the US presidential elections in November, Mr Bush will adopt a less triumphalist and unilateralist tone in light of the chaos in Iraq.

Diplomats have spent days negotiating the fine print of a joint communiqué designed to bury differences between the two sides, particularly over how they intend to tackle terrorism and its root causes.

The deeper difficulties lay at Nato, where France had reservations over a request from the Iraqi interim government to help in the training of its security forces, and for "technical assistance". After two rounds of tense discussions between Nato ambassadors, alliance diplomats said agreement was within reach.

One sensitive point was whether training would be inside or outside the country, as assistance away from Iraq is politically less sensitive for France and Germany, who opposed the war.

With Mr Bush's domestic popularity hit hard by the continuing crisis in Iraq, both Paris and Berlin are unlikely to want to help Mr Bush out of problems they say were created in the run-up to November's presidential elections. However, countries which want a wider Nato role in Iraq, including the US, the UK, Italy and Poland, are pressing for help inside the country.

A senior Nato diplomat said: "It stands to reason, if the challenge is to train the new Iraqi armed forces, that the vast majority of the training would have to take place inside Iraq, because that is where the Iraqi soldiers are."

Nato leaders will also be asked to provide resources to extend the security mission beyond Kabul to five new areas of the country, and shore up the political commitment to help stabilise Afghanistan.

Before he left for Europe, President Bush acknowledged it was unlikely the Nato summit would go as far as the US originally wanted and share much of the military burden in Iraq. "I am not so sure we're going to get more troops out of any Nato countries," he said, adding: "I think most of the Nato countries that have participated with troops are at their limit, and I think some of the Nato countries that haven't put troops in are really not interested in doing so."

Sixteen Nato nations have forces in Iraq. Some, such as Poland, are anxious to scale down their deployment.