The US embassy in Cairo has been in contact with a "large number" of Egyptian opposition members during the mass protests, but not the Muslim Brotherhood, a senior US administration official told AFP.
The official, who spoke on condition of anonymity, did not say which opposition members had been contacted, but Margaret Scobey, the US ambassador in Cairo, spoke Tuesday to top dissident Mohamed ElBaradei.
"Embassy has been in touch with a large number of people, but I don't know all the names for sure. However, Muslim Brotherhood -- no," the official said in email exchange when asked about US contacts with the opposition.
The official did not make clear why Washington has not had contacts with the Muslim Brotherhood even though it is encouraging a democratic transition in Egypt amid Egyptian calls for the ouster of President Hosni Mubarak.
But analyst Marina Ottaway said "there is a fear in the United States that the Muslim Brotherhood could gain power and that a change in leadership will impact Egypt's relations with Israel."
"Both of these fears are greatly exaggerated," she said on the website of the Carnegie Endowment for International Peace, where she works.
The opposition to Mubarak's embattled regime is a divided and diversified group of secular and Islamist parties, as well as civil society organisations.
Although the Mubarak government has formally banned it, the Muslim Brotherhood is considered the strongest grass roots movement and the most organized.
After a surprise win in 2005 elections, in which it secured 20 percent of seats (88 seats), its representation in the legislative was wiped out in the 2010 elections.
The most prominent opposition party is the New Wafd, founded in 1978 and inspired by the original Wafd party, the largest nationalist party since it was established at the start of the 20th century.
There is also al-Ghad (Tomorrow) Party, which was founded by Ayman Nur, an opposition figure who challenged Mubarak in the 2005 presidential elections.
In addition, there are several groups that left-leaning, socialists or Nasserists -- inspired by the policies of the late popular President Gamal Abdel Nasser.