By Jim Muir
BBC News, Baghdad
Iraqi Vice-President Tariq al-Hashemi vetoed a law crucial to the poll
The general elections planned for January in Iraq have been thrown into doubt by the vetoing of a long-delayed election law by the country's Sunni Vice-President, Tariq al-Hashemi, and by a threatened boycott by the Kurds in the north - which could turn out to be a more serious problem.
In theory, the crisis generated by Mr Hashemi's veto could be resolved swiftly, allowing the law to be amended by parliament and endorsed by the presidency, and an election date promulgated.
The vice-president himself said his objection was not to the law as a whole but only its first article, which he wants changed to allow a bigger allocation of seats for the four million Iraqis - many fellow Sunnis - whom he says fled the country during the violence.
Mr Hashemi said that during the 10 days of intensive to-ing and fro-ing that preceded his veto, he had been assured that parliament would settle the matter without delay.
It would, he said, take only one quick session, and need not hold up the election process.
But the Independent High Electoral Commission (IHEC), which runs the polls, took a less sanguine view.
Its patience already severely strained by weeks of delays and flouted deadlines over the passing of the revised election law, it announced that it was suspending all preparations for the polls.
This included registering candidates and drawing up ballot papers, although background activities such as training would continue.
Prime Minister Nouri al-Maliki also took the matter far less lightly than Mr Hashemi had indicated it should be.
The veto was, he said, a serious threat to the political and democratic process, and had no solid constitutional basis.
He urged IHEC to resume preparations.
But Mr Hashemi's demands seemed to be regarded as reasonable by a considerable spectrum of political opinion, including the Kurdish president, Jalal Talabani, and Shia Vice-President Adel Abd al-Mahdi.
Mr Talabani said he and Mr Abd al-Mahdi shared Mr Hashemi's reservations about the new law, but had approved it for fear of delaying the election and creating a constitutional vacuum.
There is still no final date for the proposed January election
He said Mr Hashemi was within his rights to exercise his veto.
Some Iraqi political observers believed a compromise on seats for the expatriates could be reached quite easily and quickly, although parliament's track record of fractiousness and procrastination discourages optimism.
If that were the only issue and it were indeed to be resolved swiftly, elections could still take place towards the end of January.
IHEC has said that to prepare for polling it needs a clear 60 days after the promulgation of a presidential decree announcing the date, a step that would follow after parliamentary approval of the amended law.
No final date had been set for the election by the time of Mr Hashemi's veto, although the days most mentioned are the 18 or 21 January.
So, if the law was to be amended and approved within the next week or so, a January election would still be feasible.
But the objections raised by the Kurds might be a much more serious threat to the election process, depending on how seriously they are pushed.
On Tuesday, the office of Iraqi Kurdistan's President, Massoud Barzani, issued a blistering statement threatening to boycott the elections altogether unless the region's three provinces were granted a fair share of the seats in the Baghdad parliament.
Under the revised election law the number of seats for the new chamber was set to rise from 275 to 323, to allow for population growth.
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The new seats were distributed around the provinces which, under the new law, will act as parliamentary constituencies.
Basra was allocated an extra eight seats and Nineveh (Mosul) province an additional 12.
The Kurds had been expecting something like 17 for the three provinces that make up their autonomous region.
But they were given only three.
The statement from Mr Barzani's office angrily denounced this as an attempt to minimise the Kurdish voice in Baghdad and deprive the Kurds of the gains they had made.
It also attacked the new mechanism adopted by Article 1 of the new election law for estimating the population - based, in the absence of a recent census, on ration cards issued by the Ministry of Trade.
Seats are allocated on the basis of one for every 100,000 citizens.
Since Mr Hashemi's concerns also involve Article 1 of the new law - and that will be the focus of parliamentary attention - it would be surprising if the Kurds did not raise their objections when the issue is opened in the chamber.
"Hashemi's problem is very easy to solve, but Barzani's is almost impossible," said a veteran Iraqi observer, predicting that Arab parties would resist any Kurdish attempt to revive the system adopted in the 2005 election, whereby population was estimated on the basis of census figures from the Ministry of Planning.
A Kurdish boycott would effectively scupper the elections.
While provincial elections were held last January in all of Iraq except Kurdistan, that formula could not be repeated with a general election for both political and constitutional reasons.
Nouri al-Maliki and Barack Obama both want the polls to succeed
So wrangling over a solution that would satisfy both Mr Hashemi's demands and those of the Kurds could go on for a long time, possibly making it necessary to push elections back so far that constitutional issues would be raised.
That would also start ringing alarm bells for the Americans, who had heaved a sigh of relief with the passing of the long-awaited new law by parliament on 8 November, only to find it cast into doubt again.
For Washington, the holding of credible, timely and trouble-free elections would be an important marker of stability allowing it to begin withdrawing combat troops, all of whom President Obama would like to have leave Iraq by the end of August next year, leaving only about 50,000 training and support forces.
While Washington expressed disappointment, US military commanders are putting a brave face on the political setback, with the senior coalition officer, Gen Ray Odierno, saying that withdrawal decisions would not have to be taken until April or May.