The identities of two Iranians whose arrest in Kenya this week preceded a U.S. alert of a planned "terrorist attack" in the country are not yet known, authorities in Tehran said on Saturday.

"The identities of these persons are not yet known to us and the Iranian embassy in Nairobi is seeking to obtain information and a consular visit," foreign ministry spokesman Ramin Mehmanparast said, quoted by state news agency IRNA.

Vendors of Apple products in Iran on Saturday scoffed at U.S. media reports that the consumer technology giant was banning U.S. sales to customers of Iranian background, pointing out that iPads and iPhones are widely available in Tehran.

One salesman who gave only his first name, Hossein, told Agence France Presse that he had sold 40 iPhones the day before, and explained that prices for Apple items in Iran were only around $50-$60 more than in the United States.

The "dysfunction" in the U.S. Congress, where Republicans and Democrats have failed to compromise on debt reduction, threatens U.S. national security, according to Defense Secretary Leon Panetta.

"One my greatest concerns as secretary is the dysfunction that we see in Washington," he said late Thursday at a ceremony in which he received an award for public service.

The United States on Thursday designated three leaders of the Boko Haram Islamic militant group as terrorists in a bid to stem the mounting violence in Nigeria.

A U.N. expert on Tuesday urged Washington to clarify its rules on hunting Taliban and other suspects amid a "dramatic increase" in the use of drone attacks.

The U.S. government has carried out targeted killings in countries including Afghanistan, Pakistan, Somalia and Yemen in raids and airstrikes and used unmanned drones, a report by investigator Christof Heyns said.

The Pentagon expressed serious concern Monday after the Egyptian military declared sweeping new powers just as ballots were being counted in a pivotal presidential vote.

"We're deeply concerned about new amendments to the constitution declaration, including the timing of their announcements as polls were closing for the presidential election," spokesman George Little told reporters.

North Korea accused the United States Monday of building up military forces in the region and vowed to strengthen its own defenses "in every way".

The comments came one day after the communist state said it would bolster its nuclear deterrent in the face of what it called U.S. antagonism.

The White House renewed calls Saturday for Bashar Assad to step down at a "critical juncture" in Syria after U.N. observers suspended their mission, saying it was discussing the way ahead with allies.

The unarmed observers have been targeted almost daily since deploying in mid-April to monitor a U.N.-backed but widely flouted ceasefire brokered by international envoy Kofi Annan, and they were likened to "sitting ducks in a shooting gallery" by Susan Rice, the U.S. envoy to the United Nations.

The United States hailed Yemen on Saturday for retaking militant bastions in the south of the country from al-Qaida fighters.

Yemeni troops took control of the city of Shuqra on Friday, the last major stronghold of al-Qaida in the Arabian Peninsula (AQAP) in Abyan province to fall to government forces, which launched an all-out offensive last month that has already resulted in the recapture of the towns of Jaar and Zinjibar.

Chief Palestinian negotiator Saeb Erakat will meet here next week with U.S. Secretary of State Hillary Clinton in a bid to try to breathe new life into stalled peace talks, a U.S. official said Friday.

Clinton had already met with Israeli negotiator Yitzhak Molho and "she'll see Erakat next week," State Department spokeswoman Victoria Nuland said.