The U.N. Security Council was poised Saturday to unanimously approve a new package of modest sanctions against Iran, including a ban against Iranian arms exports and financial restrictions against an expanded list of officials and companies — that world powers hope will still send a strong message that Tehran will only further isolate itself by refusing to suspend uranium enrichment.

Iran has vowed the sanctions will only motivate it further to pursue nuclear power, a message Iranian Foreign Minister Manouchehr Mottaki was expected to deliver in an address to the Security Council before the vote.

Mottaki was making the trip instead of Iranian President Mahmoud Ahmadinejad, who claimed he had canceled his appearance because the U.S. failed to deliver his visa in time. The U.S. State Department denied the allegation and said visas had been issued for Ahmadinejad and members of his delegation.

The six world powers that drafted the new sanctions resolution spent Friday trying to overcome objections from several council members, reflecting concerns that anything short of consensus would weaken efforts to rein in Iran's nuclear defiance.

There were several minor concessions but no changes to the key sanctions agreed upon last week by the United States, China, Russia, Britain, France — all permanent members of the Security Council — and Germany. Those include banning Iranian arms exports and freezing the assets of 28 additional people and organizations involved in Iran's nuclear and missile programs. About a third of those are linked to the Revolutionary Guard, an elite military corps.

The new sanctions — already a compromise between the stronger measures favored by the United States, Britain, France and Germany and the softer approach advocated by Russian and China — are considered modest. The ban on exports is among the harshest measures, but many of Iran's arms sales may not be affected because they are illicitly sent to militant groups like Lebanon's Hezbollah and Shiite militias in Iraq.

Still, world powers hoped that approving the resolution quickly and unanimously would signal that Iran will face stricter sanctions each time it ignores a Security Council deadline to suspend uranium enrichment, a process that can be used to produce nuclear energy or weapons. The council imposed its first set of sanctions in December, but Iran responded by expanding uranium enrichment. Iran has insisted its nuclear program is for peaceful purposes.

The latest sanctions are "serious measures that underscore the severity with which the council views rejection of its resolutions," acting U.S. Ambassador to the U.N. Alejandro Wolff said. He warned that if Iran continues to defy Security Council demands "we will continue to add measures and continue to up the pressure."

Adding to tensions, the Iranian military questioned 15 detained British sailors and marines in Tehran Saturday and said they had confessed to illegally entering Iranian waters in an act of "blatant aggression." Britain has demanded the return of the sailors and marines and denied they had strayed into Iranian waters while searching a merchant ship just outside the mouth of a channel dividing Iraq from Iran.

European Union foreign policy chief Javier Solana said the incident must not complicate the push to impose further sanctions on Iran.

"The resolution will follow its course," Solana told journalists at an EU summit in Berlin. "It will probably be approved ... It would be a tremendous mistake if these two things were mixed."

Iran says it will never give up its right under the nuclear non-proliferation treaty to enrich uranium and produce nuclear fuel, although it has offered to provide guarantees that its nuclear program won't be diverted toward weapons, as the U.S. and some of its allies fear.

Ahmadinejad had said he wanted to make those arguments himself before the Security Council, but Iran accused the United States of thwarting his planned trip by delaying the delivery of his visa. U.S. State Department deputy spokesman Tom Casey said the visas for Ahmadinejad and his delegation had arrived in plenty of time and suggested the Iranian president was "unwilling to stand before the Council and take the heat for his continued defiance of the international community."

Iranian leaders kept up their defiant rhetoric in the days leading up to the vote, with Ahmadinejad calling the Security Council illegitimate and Supreme Leader Ayatollah Ali Khamenei suggesting Iran would pursue nuclear activities outside international regulations if faced with more sanctions.

In December, the Security Council ordered all countries to stop supplying Iran with materials and technology that could contribute to its nuclear and missile programs and to freeze assets of 10 key Iranian companies and 12 individuals related to those programs.

The new resolution would call for voluntary restrictions on travel by the individuals subject to sanctions, on arms sales to Iran, and on new financial assistance or loans to the Iranian government.

It asks the U.N.'s nuclear watchdog body, the International Atomic Energy Agency, to report back in 60 days on whether Iran has suspended enrichment and warns Iran could face further measures if it does not. But it also says all sanctions will be suspended if Iran halts enrichment and makes clear that Tehran can still accept the package of economic incentives and political rewards offered last year if it complies with the council's demands.

The latest resolution met with surprising resistance from several elected non-permanent Security Council members who complained their views were not getting enough consideration from the five veto-wielding permanent members, .

In a key compromise, the document will refer to a past resolution from the IAEA calling for the Middle East to be free of weapons of mass destruction. Indonesia and Qatar had wanted the council to make that appeal outright, but that would have had implications for Israel, a U.S. ally widely believed to possess nuclear weapons, although it has never officially acknowledged it.