"They realise that if they make such a mistake the retaliation of Iran would be severe and they will repent," Ahmadinejad said.
"All people know they cannot strike us. Iran is capable of defending itself. It is a strong country," he added.
The West cannot stop Tehran from pursuing its nuclear energy programme, he said. "Superpowers cannot prevent us from owning this energy."
The United States, which has a strong military presence in the Gulf, accuses Iran of wanting to produce nuclear weapons and has sought tougher UN sanctions against Tehran.
Iran says it wants only to generate electricity to allow more oil exports.
Using stronger language than on Sunday when he called for US troops to leave the region, Ahmadinejad said Gulf countries should "get rid of" foreign forces, which he blamed for regional insecurity.
"We in the Persian Gulf are faced by difficulties and enemies. Those do not want the region to live in safety ... peace can be achieved by getting rid of these forces," he said.
"They intervene in the region and make it insecure. They claim that lack of security is the reason for their presence (but) the problem is the intervention of foreign powers."
Iraq talks
Ahmadinejad said Iran had agreed to talk to the United States about Iraq to help the Iraqi people.
"The Americans, in order to solve the security situation in Iraq, requested to talk to Iran. In order to support the Iraqi people we will talk to them," he said.
"It (the meeting) will take place in Baghdad in the presence of the Iraqi government," he said, adding that a date for the talks had yet to be set.
The White House said on Sunday that US and Iranian officials would meet in the next few weeks in Baghdad about security in Iraq, confirming a similar announcement by Tehran.
Ordered out
Al Jazeera was ordered out of the press conference.
Iran banned Al-Jazeera from its parliament last week, saying one of its talkshows had insulted the most revered Shia cleric in Iraq.
Mohammad al-Abdullah, Al Jazeera's correspondent in Abu Dhabi, said officials from the Iranian embassy in the UAE had asked the Arabic and English-language Al Jazeera teams to leave the hall ahead of the press conference.
"Al Jazeera team in the UAE was told two days ago that the Iranian side did not want Al Jazeera to attend Ahmadinejad's press conference," al-Abdullah said.
"However, the UAE side said on Sunday night that both Al Jazeera's Arabic and English teams were allowed to attend the conference."