The US administration is expected to formally tell Congress of a planned $20bn arms deal with Saudi Arabia, after George Bush, the US president, arrived in the Arab state as he nears the end of his Middle East tour.
The official announcement, expected on Monday, will start a 30-day review period during which Congress could try to block the deal.
The deal, which includes satellite-guided weaponry and high-tech munitions, has alarmed Israel and some US Congressmen since it was unveiled last July, especially as Saudi Arabia refuses to recognize the Jewish state.
During his visit to Saudi Arabia, his first visit to the oil-rich US ally, Bush hopes to rally support for his campaign to isolate Iran.
His administration, which has also announced a $30bn military aid pact with Israel, has argued the deal with the Saudis is needed to counter what it claims is a "major security threat" from Iran.
A senior US official said Bush will court Riyadh's diplomatic influence and financial muscle which "could make an enormous difference in places like the Palestinian territories, Lebanon, Iraq, Afghanistan and other locations".
While Sunni-ruled Saudi Arabia has voiced concern over the rise of Shia Iran, it is opposed to another war after the 2003 US-led invasion of Iraq that has strengthened the Islamic regime in Tehran.
Diplomatic tour
In the last few days of his Middle East tour, Bush has been courting Gulf Arab allies to help shore up a US-backed peace effort between Israel and the Palestinians and combat Iran's growing influence in the region.
Saudi Arabia is considered a linchpin for any broader Israeli-Arab reconciliation as Bush presses Israelis and the Palestinians to secure a peace deal before he leaves office in January 2009.
Iran was also expected to be an important part of Bush's talks with King Abdullah, the Saudi monarch, and was also discussed in Bush's earlier meetings with Gulf Arab leaders in the UAE.
While the Gulf leaders share US concerns about curbing their powerful Shia neighbor, they want to avoid another war in the region.
"All agreed it's a difficult problem that needs to be addressed, and at this point pursue in a diplomatic fashion," Hadley told reporters when asked how UAE leaders had reacted to Bush's entreaties on Iran.
Engaging Iran
Analysts say there are growing signs that America's Arab allies prefer to engage Iran.
Last year, Saudi Arabia invited Mahmoud Ahmadinejad, the Iranian president, to undertake the Hajj, making him the first Iranian president to receive an official invitation to the annual Muslim pilgrimage.
Also in the region on Monday, was Nicolas Sarkozy, the French president, who visited Qatar and was later to travel to the UAE.
At the start of his regional tour, Sarkozy also met kind Abdullah in Saudi Arabia, where he offered Saudi Arabia help in developing peaceful nuclear energy.
The French president expects to sign a nuclear co-operation agreement in with the UAE on Tuesday.
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George W Bush