US President Barack Obama warned on Tuesday that if Russia sold an advanced missile defense system to Iran, the United States could "penetrate" Tehran's stockpile if needed. Speaking on the MSNBC program "Hardball with Chris Matthews," Obama underlined that the US objected to Russia's decision to lift a ban on the sale to Iran of the S-300 air-defense missile system. The US president said the move was of particular concern due to the ongoing negotiations between world powers and the Islamic Republic on a final deal regarding Iran's disputed nuclear program."Our defense budget is somewhere just a little under $600 billion. Theirs is a little over $17 billion. Even if they’ve got some air defense systems, if we had to, we could penetrate them," he said on the MSNBC program.Turning to the conflict in Yemen, Obama also warned Iran not to send weapons to rebels in the embattled state that could be used to threaten shipping traffic in the region."What we've said to them is that, 'If there are weapons delivered to factions within Yemen that could threaten navigation, that's a problem,'" he said. "And we're not sending them obscure messages. We send them very direct messages about it," Obama told MSNBC.Washington wants to maintain pressure on the Yemen-based al-Qaida in the Arabian Peninsula, one of the militant movements most active groups, which it fears may take advantage of the chaos to extend its grip and plan further attacks on the West.The president added that the region was in a state of transition and that Washington would be paying very close attention."I think the Islamic world is going through a process where they have to isolate and push out the kind of extremism that we've seen expressed by ISIL."The United States said on Monday an aircraft carrier and guided-missile cruiser had gone to the waters off Yemen to join seven other US warships already in the area.The US said their presence in the region was to help prevent conflict."One of our goal as the world's leading superpower is to work with partner countries to try to resolve conflicts, to be ruthless in going after terrorism. But we're not gonna do that by ourselves, and we're not gonna do it just by deploying more Marines in every country that has these problems."The Pentagon said the ships were there to ensure freedom of navigation through the area, which is vital to oil shipping and controls approaches to the Red Sea and the Suez Canal.It said the ships were also watching a flotilla of Iranian cargo vessels that had approached Yemen. The UN Security Council has imposed an arms embargo on the Houthis, and the Saudi navy has imposed a naval blockade around the country.