The Pentagon has ordered military commanders to develop new options for attacking Iran, CBS reported Tuesday, as a second US aircraft carrier steamed into the Persian Gulf. According to the report, the planning was being driven by what one officer called the "increasingly hostile role" Iran is playing in Iraq - smuggling weapons into Iraq for use against American troops. Secretary of Defense Robert Gates said that "what the Iranians are doing is killing American servicemen and -women inside Iraq." CBS said that US officials were also concerned by Iranian harassment of US ships in the Persian Gulf as well as Iran's still growing nuclear program. The television channel cited new pictures of Iran's uranium enrichment plant which showed the country's defense minister in the background, in an apparent deliberate attempt to mock the recent New Intelligence Estimate which said Iran had ceased work on a nuclear weapon. Last week, Joint Chiefs of Staff Mike Mullen warned Iran not to assume the US military can't strike. Targets would include everything from the plants where weapons are made to the headquarters of the organization known as the Quds Force which directs operations in Iraq, CBS reported. Later this week Iraqi Prime Minister Nouri al-Maliki is expected to confront the Iranians with evidence of their involvement in fueling the Iraq insurgency and demand a halt. If that doesn't produce results, continued the report, the State Department has begun drafting an ultimatum that would tell the Iranians to cease their activities - or else. Gates said Tuesday that sending a second US aircraft carrier to the Persian Gulf could serve as a "reminder" to Iran, but he said it's not an escalation of force. Speaking to reporters after meeting with Mexican leaders, Gates said heightening US criticism of Iran and its support for terror groups is not a signal that the administration is laying the groundwork for a strike against Teheran. Still, he said Iran continues to back the Taliban in Afghanistan. "I do not have a sense at this point of a significant increase in Iranian support for the Taliban and others opposing the government in Afghanistan," Gates said. "There is, as best I can tell, a continuing flow, but I would still characterize it as relatively modest." Gates played down the addition of a second carrier to the Gulf, saying that the number of ships there rises and falls continuously. He said he doesn't expect there to two carriers there for a long time. Asked if the carrier move went hand in hand with the rising US rhetoric against Iran, Gates said, "I don't see it as an escalation. I think it could be seen, though, as a reminder." In recent weeks, US officials have ratcheted up their complaints that Iran is increasing its efforts to supply weapons and training to militants in Iraq. Military commanders in Baghdad are expected to roll out evidence of that support soon - including date stamps on newly found weapons caches showing that recently made Iranian weapons are flowing into Iraq at a steadily increasing rate. Another senior military official said the evidence will include mortars, rockets, small arms, roadside bombs and armor-piercing explosives - known as explosively formed penetrators or EFPs - that troops have discovered in caches in recent months. The official, who spoke on condition of anonymity because the evidence has not yet been made public, said that dates on some of the weapons were well after Teheran signaled late last year that it was scaling back aid to insurgents. Speaking of Afghanistan on Tuesday, Gates said that the Taliban is changing its tactics there - from large-scale firefighters to a "significant increase in terrorist acts," including roadside bombs and suicide attacks, similar to the one that unsuccessfully targeted Afghan President Hamid Karzai on Sunday. At least one police officer has been arrested in connection with the assassination attempt, deepening concerns about the Taliban's infiltration of Afghan security forces. Gates said, however, he does not have a sense that the infiltration is any worse that it has been before. He said that it is important to screen the security forces well and that military trainers working with those forces need to make that a focus of their efforts.