Reports in Washington suggest that Pakistan has made its willingness to support the US conditional on the exclusion of both Indian and Israeli forces from any combined military action against Afghanistan. Pakistan's ambassador to the US and the Secretary of State, Mr Colin Powell, both refused to confirm the report, but both spoke of the need to take account "regional sensitivities".
In building international support for its retaliation against Osama bin Laden and for a global alliance against terrorism, sensitivities abound. Even the US's strongest allies are urging caution in its military response.
The US has made a remarkable first few steps in going beyond mere expressions of solidarity. Pakistan and Russia have agreed to share intelligence on bin Laden and appear willing to go much further in supporting attacks. Pakistan is expected to agree to US planes using its airspace but not to the presence of ground troops.
Russia, although unwilling to see US attacks from its soil, has been very supportive of a struggle against the Taliban, not least because of Taliban influence on militants in Chechnya.
Within Afghanistan, the alliance of factions fighting the Taliban has offered military support and appealed for military supplies.
The attacks also appear to have opened up a real rapprochement with the pariah state of Iran, whose Shia leadership is bitterly opposed to the Sunni Taliban.
The country has closed its 560-mile border with Afghanistan and the US has welcomed the unexpectedly warm expressions of sympathy from Tehran.US sources say, however, that the best they can expect is that Iran would stand idly by.
One of Afghanistan's neighbours, Uzbekistan, itself a victim of a wave of bombings by Islamic extremists in 1999, has been a regional leader in battles against Islamic militants both at home and next door.
President Islam Karimov said on Sunday that he was open to Uzbek territory being used for a launch pad for a US attack, despite threats from the Taliban to retaliate.
Tajikistan, however, has not been so forthcoming.
But even among its closest allies in Europe and NATO, support for the US will not be unqualified. Among the EU member states, both Belgium and Italy have made clear they are not at war, while Spain, on the other hand, has offered its airbases unconditionally.
Britain is likely to be most supportive, while Germany's President Gerhard Schr÷der over the weekend went out of his way to make sure journalists understood that the NATO statement last week did not mean a binding commitment to joining in military action.
France's Foreign Minister, Mr Hubert Vedrine, also sounded a cautious note on Sunday, saying it was important to avoid a "clash of civilizations" between the West and Islam in the wake of the attacks.
"I have good reason to hope that American leaders can come up with a strong and justified response to what has happened without falling into the diabolical trap conceived by the instigators of the assault," Mr Vedrine said.
In the case of Ireland, the Taoiseach has made it clear that the US cannot expect unconditional support.
With only days to go before Ireland assumes the chair of the Security Council, Mr Ahern emphasised that any US action must be sanctioned by the UN and in conformity with its rules.
Such an approach, likely to be followed by several EU states as well as many second- and third-world countries, reflects more than a philosophical commitment to the UN as an arbiter, however imperfect, of global disputes.
The political reality is also that if the US has to legitimise its actions through the UN it is likely to be more measured and discriminate in its actions.
In an interview with the Washington Times yesterday, Egypt's President Hosni Mubarak, a key figure if the US is to win broad Arab support, warned that plans for a coalition of nations "would simply divide the world between those who are part of the coalition and those who are not - and thus fail to reach the objective".
He called for the convening of a UN summit to draft and sign a binding counter-terrorism treaty.
And Mr Mubarak warned of the precariousness of the US position because of perceptions in the region of its continued uncritical support for Israel.
"Go to all the so-called moderate states in the region, from Jordan to Saudi Arabia, Kuwait, Qatar, the UAE, and Oman: their leaders have told that their streets are on the verge of boiling over."
Meanwhile Israel's Prime Minister, Mr Ariel Sharon, said yesterday that Israel would not make concessions to the Palestinians to facilitate US efforts to recruit Arab and Islamic countries to an anti-terror alliance.
The US has pushed for truce talks to end Israeli-Palestinian fighting. "The Arab countries now will certainly try to use this opportunity to pressure Israel and say that what is bothering them is that Israel did not give concessions to the Palestinians," Mr Sharon told the Jerusalem Post.
But, he said, Israel would not "pay the price" for the formation of an anti-terrorism coalition.
Meanwhile, the Security Council has arguably already given the US an unusual degree of discretion, both in terms of its right to use force and of who that force may be directed against.
The resolution, agreed unanimously on Friday, starts by reflecting a UN determination to combat terrorism "by all means", and the Charter right of the US to self-defence.
It calls "on all states to work together urgently to bring to justice the perpetrators, organizers and sponsors of the terrorist attacks and stresses that those responsible for aiding, supporting or harbouring the perpetrators, organisers and sponsors of these acts will be held accountable."
And, crucially, it expresses the UN's "readiness to take all necessary steps to respond to the terrorist attacks of 11th September 2001 and to combat all forms of terrorism".
In the past, most notably in the Balkans, the US and its allies have used a significantly weaker formulation to argue that bombing had been pre-sanctioned by the UN. Should the Chinese or other permanent member of the Security Council with veto power back-track and refuse to sanction specific action, US diplomats still have substantial UN cover.
A top Chinese security official issued a veiled warning to Washington yesterday against military retaliation for last week's terror attacks, saying it would only "aggravate terrorism and violence". Mr Xue Dongzheng also suggested at an international conference that the US should shoulder some blame for terrorism, which he said was caused in part by "alien intervention".
"Instead of alleviation, this could only aggravate terrorism and violence," he told a meeting of police, security and judicial officials at an Asia-Europe Meeting.
Such reservations are unlikely to stop the US from taking action, but may well reflect early signs of the sort of diplomatic problems it will face once it moves to seek more than general declarations of support.