Kurdish parties warned Wednesday that they might bolt Iraq's new government if Shiites (search) gain too much power. In another challenge to the interim administration, saboteurs blew up an oil pipeline, forcing a 10 percent cut in electricity output.

Kurdish fears of Shiite domination rose after the Americans and British turned down their request to have a reference to the interim constitution — which enshrines Kurdish federalism — included in the U.N. resolution approved Tuesday.

The country's most prominent Shiite leader, Grand Ayatollah Ali al-Husseini al-Sistani (search), rejected any mention of the interim charter in the resolution. Shiites oppose parts of the charter that give Kurds (search) a veto over a permanent constitution due to be drawn up next year.

Meanwhile, clashes persisted Wednesday around Fallujah, a rebellious Sunni Muslim city west of Baghdad. Four members of an Iraqi force given control of the city last April were wounded when a mortar round exploded.

The pipeline attack appeared to be part of an insurgent campaign against infrastructure to shake confidence in the new government, due to take power on June 30.

The blast occurred about 9:30 a.m. near Beiji, 155 miles north of Baghdad, said Col. Sarhat Qadir of the Kirkuk police. Huge fireballs rose into the air, witnesses said.

Oil Ministry spokesman Assem Jihad told Dow Jones Newswires that the attack would not effect exports from the northern oil fields. However, the blast cut supplies to the Beiji electric power station, forcing a reduction of 400 megawatts in power generation, Jihad said.

Iraq now produces around 4,000 megawatts. Power cuts in the country have now reached more than 16 hours a day, making it difficult to cope with soaring heat, which is already more than 100 degrees.

The U.S.-run coalition had made its ability to guarantee adequate electricity supplies a benchmark of success in restoring normalcy to Iraq. However, sabotage and frayed infrastructure have impeded efforts to eliminate power outages, especially in the capital.

Coalition officials fear that insurgents may step up attacks on infrastructure targets to undermine public confidence both in the U.S. occupation authority and the new regime.

The new U.N. resolution, adopted unanimously by the Security Council, affirmed international support for the new Iraqi government.

Both major Kurdish parties — the Kurdistan Democratic Party and the Patriotic Union of Kurdistan — conferred Wednesday to consider a response to the decision not to refer to the interim constitution in the resolution. The interim charter, adopted in March, affirms the principle of federalism.

Kurds fear that the interim constitution, which the Americans hailed as the most progressive in the Middle East, will be sidelined once the occupation ends and the Shiite clergy gains ascendancy.

The Kurds have been running their own autonomous mini-state since 1991, and many Kurds would prefer their own independent country.

At the United Nations, Secretary-General Kofi Annan sought to reassure the Kurds, saying that while the resolution doesn't refer to the constitution, it "does have language that refers to a united federal democratic Iraq."

Diplomats said reference to the interim constitution was omitted because of opposition by al-Sistani. Shiites are believed to compromise about 60 percent of Iraq's 25 million while Kurds number around 15 percent.

In a statement addressed to the U.N. Security Council earlier this week, al-Sistani warned that mentioning the interim charter in the resolution would be "an act against the will of the Iraqi people and will have dangerous results."

Iraq's Foreign Minister Hoshyar Zebari, the first Kurd to hold the post, said he had lobbied unsuccessfully for an acknowledgment of the charter during his meetings at the Security Council last week.

But he said he was satisfied that the "spirit" of the charter was in the final resolution.

Still, Kurdish leaders in Iraq were unconvinced.

"Now our future is ambiguous," said Nesreen Berwari, a Kurdish member of the interim government. "The interim constitution would have been the clear and bright roadmap to the all components of the Iraqi people."

Berwari said she would resign if asked to do so by the Kurdish leadership.

"Until now, we have not called for a separate Kurdistan, but if the Kurds' rights are not recognized, then we will take political measures that serve the interests of the Kurdish people," said Mulaha Bekhtiyar of the PUK. "For the time being, we will commit to a united Iraq."

Bekhtiyar said that the Kurds would not agree to the Shiites having the "lion's share" of any government.

Meanwhile, some Iraqis welcomed the new resolution, which the United States and Britain had to repeatedly alter to accomodate demands that the interim government be given greater authorities. Iraqis have worried that the continued presence of U.S.-led troops will limit what is supposed to be the new administration's full sovereignty.

"Full sovereignty won't come overnight particularly because Iraq has been subject to threats and terrorist acts," said Baghdad resident Tareq Rasheed. "As far as I'm concerned, the troops could stay, but outside the cities, until the government is able to control security."

But another Baghdadi was against any foreign interference in Iraq. "I don't welcome any resolution issued by the Security Council regarding Iraq. All their resolutions are fabricated and they impose them on the Iraqi people," Abdul-Karim Hassan said.

In other developments:

— A group holding two hostages — a Turk and an Egyptian — threatened to kill the captives after Friday prayers unless their home governments condemn U.S. actions in Iraq. The threat was made in a statement distributed in Fallujah.

— Insurgents attacked a Baghdad city council member Tuesday, wounding him and killing two of his bodyguards, the military said. The incident is under investigation.