US Secretary of State Condoleezza Rice has warned that Iran poses the biggest threat to US Middle East interests, as she begins a major regional tour.

Ms Rice and US Defence Secretary Robert Gates are meeting Egyptian President Hosni Mubarak and Arab ministers at the Red Sea resort of Sharm el-Sheikh.

The meeting comes after Washington confirmed plans for a massive arms deal for the region.

The tour is aimed at uniting US allies against Iran, Syria and Hezbollah.

Ms Rice denied Iranian claims that US policies were spreading fear in the Middle East.

Iranian foreign ministry spokesman Mohammad Ali Hosseini had accused the US of tarnishing good relations between countries of the region.

Iran's nuclear programme and influence among Shia Muslim militant groups have long been sources of US concern.

During a stop-over in Shannon, Ireland, Ms Rice told reporters: "There isn't a doubt, I think, that Iran constitutes the single most important, single-country challenge to... US interests in the Middle East and to the kind of Middle East that we want to see."

The trip is the two officials' first joint tour of the region.

They will visit Egypt and Saudi Arabia together, and other countries separately.

Mr Gates told reporters travelling with him that US officials wanted "to reassure all of the countries that the policies that (US President George W Bush) pursues in Iraq have had and will continue to have regional stability and security as a very high priority".

Congressional opposition

The main beneficiaries of the deals are Israel, Egypt and Saudi Arabia.

The $30bn aid to Israel over 10 years represents a 25% increase from present levels.

The Jewish state said the package would allow it to maintain its military "qualitative edge" in the region.

The sale of satellite-guided bombs to Saudi Arabia, the first such sale to any Arab country, is thought to be part of the proposed $20bn arms deal with the kingdom and give other Gulf states - the United Arab Emirates (UAE), Kuwait, Qatar, Bahrain and Oman.

During their lobbying tour of the region, Ms Rice and Mr Gates are expected to ask Saudi King Abdullah to do more to support the Iraqi government of Iraqi Prime Minister Nouri Maliki.

The US ambassador to the United Nations, Zalmay Khalilzad, has gone as far as accusing Saudi Arabia of undermining efforts to stabilise Iraq.

The weapons deals need to be approved by Congress, and appear set to encounter opposition.

Two Democratic congressmen, Anthony Weiner and Jerrold Nadler of New York, said at the weekend they would introduce legislation to block military aid to Saudi Arabia.