By Paul Wood BBC Middle East correspondent, Jerusalem

What are the Israelis up to at the Muqata'a, as Yasser Arafat's Ramallah headquarters is known?

After all, it is not the "return address" for Thursday's Tel Aviv bus bombing. That belongs to Hamas.

The ostensible aim of the operation is to seize wanted men, including the Palestinian head of intelligence General Tawfik Tirawi.

This underlines the Israeli contention that the authors of many terror attacks are part of Mr Arafat's inner circle.

Demonstrators have taken to the streets in support of Arafat

Israeli television reports that the real aim is to make life so uncomfortable for Mr Arafat that he will leave the Palestinian territories.

That would allow Ariel Sharon and his Cabinet to avoid the difficult decision to actually expel him.

The Israeli Army is said to view the siege as a further step towards removing Mr Arafat from his position as leader of the Palestinians. This is a declared objective not only of the Israeli Government, but of Washington, too.

Popular feeling

Arafat's popularity has been slipping among his own people.

But if the Israelis hoped to destroy his authority along with his office complex, their action has served only as a rallying call for the beleaguered Palestinians.

Thousands of youths have braved the curfew and Israeli tanks to protest against any attempt to harm Mr Arafat.

The Israelis have promised this is not their intention and Israeli troops at the scene say they have been ordered not to fire at the building which houses the Palestinian leader's personal quarters.

But the psychological pressure continues. Since last Thursday night, no food and drink has been allowed in (although the Israelis have made clear they will allow food and medical supplies to be sent if necessary).

Phone lines and power are cut off from time to time.

Arafat alone

There have been no international visits - no diplomats expressing concern, no groups of singing peace activists and no journalists to hang on Mr Arafat's every word.

Instead Mr Arafat has been making a long round of telephone calls to world leaders from his desk in the Muqata'a.

The last siege was brought to and end after Crown Prince Abdullah of Saudi Arabia called President Bush, who in turned called Prime Minister Sharon.

This time around there has been strong condemnation of the Israeli siege from the Arab world and from the European Union.

President Chirac of France spoke to Mr Arafat and said he was "appalled" at what was happening.

But, crucially, there has been only half-hearted and low-level intervention from the United States.

That may change if US coalition building for a war on Iraq is damaged by Arab fury over the siege.

On Saturday, for instance, Jordan called on Israel to halt its operations in the Palestinian territories because of the threat to stability throughout the region.

Both sides are waiting to see if these international pressures to come into play.

But the Israelis assume they have a US green light to continue, at least for the time being. It could be another long stay for Mr Arafat at his desk in the Muqata'a.