By Pam O'Toole BBC regional analyst

Top officials from the six largest Iraqi opposition groups have arrived in Washington for talks with United States government officials in the biggest such meeting for several years.

Four of the six groups have sent their leaders, while the other two have sent high-ranking representatives.

The US says the talks - with State Department and Defence Department officials - will discuss the next step in co-ordinating Washington's work with the Iraqi opposition and how this relates to the overall US policy of regime change in Iraq.

But the process could still be plagued by difficulties. Not only has the Iraqi opposition been notoriously divided in the past, but future US policy on Iraq still seems unclear.

Historic meeting

It is the first time this US administration has invited all of these groups to Washington together at leadership level.

INC spokesman Sharif Ali Bin Al Hussein says Saddam has lost the army's support

Those invited include the four parties with the most presence on the ground in Iraq along with an umbrella group, the Iraqi National Congress.

The idea is to improve co-operation and co-ordination on both sides.

Some of the Iraqi delegations say they are hoping to present a united front. And they do have some common ground - the wish to overthrow Saddam Hussein and a desire for democracy in Iraq.

But there are still underlying rivalries and it is not clear how far their co-operation might stretch.

Washington also appears to be using the meeting to try to present a more united front. Previously, different arms of the Bush administration have favoured different Iraqi opposition groups as their main interlocutors.

The US is clearly hoping these talks will produce a less competitive environment.

The opposition groups will be trying to sound out the US on how it envisages an Iraq without President Saddam Hussein.

The Kurds, in particular, have said they are not prepared to participate in any American plan to topple President Saddam Hussein without clear security guarantees, including some kind of autonomy in any future system.

Another group has spoken of the need to establish a provisional government.

But the US is likely to want to keep its options open. US sources stress that this meeting is not an attempt to set up a provisional Iraqi leadership, but to establish a foundation which could act as a magnet for other opposition groups in the future.