By Michelle Nichols

UNITED NATIONS (Reuters) -Iran accused the United States of being complicit in Israel's attacks on the Islamic Republic, which Washington denied, telling Tehran at the United Nations Security Council that it would "be wise" to negotiate over its nuclear programme.

Iran launched retaliatory strikes on Israel late on Friday after Israel attacked Iran earlier in the day. Israel's U.N. Ambassador Danny Danon said Iran had been "preparing for war" and Israel's strikes were "an act of national preservation."  

His Iranian counterpart, Amir Saeid Iravani, accused Israel of seeking "to kill diplomacy, to sabotage negotiations, and to drag the region into wider conflict," and he said Washington's complicity was "beyond doubt".

"Those who support this regime, with the United States at the forefront, must understand that they are complicit," Iravani told the Security Council. "By aiding and enabling these crimes, they share full responsibility for the consequences." 

U.S. President Donald Trump said Friday that he had given Tehran a 60-day ultimatum, which expired on Thursday, to make a deal over its escalating uranium enrichment program. A sixth round of U.S.-Iran talks had been scheduled to take place in Oman on Sunday, but it was unclear whether it would go ahead.

Danon said Israel had been patient despite mounting risks.

"We waited for diplomacy to work ... We watched negotiations stretch on, as Iran made false concessions or refused the most fundamental conditions," Danon told the Security Council. He said intelligence had confirmed Iran could have produced enough fissile material for multiple bombs within days. 

Senior U.S. official McCoy Pitt said the United States will continue to seek a diplomatic resolution that ensures Iran will never acquire a nuclear weapon or pose a threat to stability in the Middle East. 

"Iran's leadership would be wise to negotiate at this time," Pitt told the council. While Washington was informed of Israel's initial strikes ahead of time it was not militarily involved, he said.

U.N. nuclear watchdog chief Rafael Grossi told the Security Council the above-ground pilot enrichment plant at Iran's Natanz nuclear site had been destroyed, and that Iran has reported that nuclear sites at Fordow and Isfahan were also attacked. 

(Reporting by Michelle Nichols, Francois Murphy and John Shiffman; Editing by Bill Berkrot, Cynthia Osterman and Daniel Wallis)