US National Security Advisor John Bolton arrived in Israel Saturday as military tensions escalated between Tehran and Washington over the shooting down of an unmanned US drone by the Islamic Republic.Iran said on Saturday it would respond firmly to any US threat, the semi-official Tasnim News Agency reported.Speaking in Washington on Saturday before heading to the US presidential retreat at Camp David, where he said he would deliberate on Iran, US President Donald Trump said the American government was imposing new sanctions on Tehran.“We are putting additional sanctions on Iran,” Trump told reporters. “In some cases we are going slowly, but in other cases we are moving rapidly.”Military action was “always on the table,” the president added, but said he was open to reversing the escalation and could quickly reach a deal with Iran that he said would bolster the country’s flagging economy.“We will call it ‘Let’s make Iran great again,’” Trump said.Bolton is in Israel to discuss Iran with Prime Minister Benjamin Netanyahu on Sunday and to participate Monday and Tuesday in an unusual trilateral meeting between US, Russian and Israeli officials.Bolton will meet with Israeli National Security Adviser Meir Ben-Shabbat and Russian Secretary of the Security Council Nikolay Patrushev.“Nice to be back in Israel. Looking forward to meeting with Israeli PM Netanyahu tomorrow & my counterparts from Israel & Russia, Meir Ben-Shabbat & Nikolay Patrushev, to discuss regional security,” Bolton tweeted upon his arrival.Prior to the trilateral summit, Patrushev met last week with the secretary of the Iranian Supreme National Security Council Ali Shamkhani, according to the Russian media.Iran’s military activity in Syria will also be under discussion at the trilateral meeting.Last week, the Russian Embassy in Israel tweeted a statement from Patrushev, in which he said, “Iran is in Syria at the invitation of the legitimate government and is actively involved in fighting terrorism. Therefore, of course, we will have to take into account the interests of Iran.”On Thursday, an Iranian missile destroyed a US Global Hawk surveillance drone. Tehran repeated on Saturday that the drone was shot down over its territory. Washington said the incident happened in international airspace.Trump said on Friday that he called off a military strike to retaliate because it could have killed 150 people, signaling that he was open to talks with Tehran.“[Iran] shot down an unmanned drone flying in International Waters. We were cocked & loaded to retaliate last night on 3 different sights when I asked, how many will die. 150 people, sir, was the answer from a General. 10 minutes before the strike I stopped it,” Trump tweeted.He continued in the tweet saying the planned US attack was not “proportionate to shooting down an unmanned drone. I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world. Sanctions are biting & more added last night. Iran can NEVER have Nuclear Weapons, not against the USA, and not against the WORLD!”Trump also blasted former US president Barack Obama’s Iran deal to limit Tehran’s nuclear capacity. The Trump administration has voided US participation in the deal that also included signatures from Russia, China, Germany, France and Great Britain.Trump’s hesitation to attack Iran sparked an intense political debate in the US that cut across party lines.Republican Florida Congressman Matt Gaetz tweeted his support of the president.“We do not need to go to war with Iran over an unmanned drone until we have more information. I am done with endless, unconstitutional regime change wars in the Middle East,” Gaetz wrote.House Speaker Nancy Pelosi said, “We are in an extremely dangerous and sensitive situation with Iran. We must calibrate a response that de-escalates and advances American interests, and we must be clear as to what those interests are.”“We have no illusions about the dangerous conduct of the Iranian regime. This is a dangerous, high-tension situation that requires a strong, smart and strategic approach,” she added.Iranian Foreign Ministry spokesman Abbas Mousavi told Tasnim said that “Regardless of any decision they (US officials) make... we will not allow any of Iran’s borders to be violated. Iran will firmly confront any aggression or threat by America.”Worries about a confrontation between Iran and the United States have mounted despite Trump saying he has no appetite to go to war with Iran. Tehran has also said it is not seeking a war but has warned of a “crushing” response if attacked.“Any mistake by Iran’s enemies, in particular America and its regional allies, would be like firing at a powder keg that will burn America, its interests and its allies to the ground,” the senior spokesman of Iran’s Armed Forces, Abolfazl Shekarchi, told Tasnim on Saturday.A senior commander of the Revolutionary Guards struck a similarly defiant note, in comments quoted by the Islamic Republic News Agency.“This is our response to a violation of Iranian space and if the violation is repeated then our response will be repeated,” said Brig.-Gen. Amir Ali Hajizadeh, head of the Guards’ aerospace division. “It’s possible that this infringement of the Americans was carried out by a general or some operators.”Pentagon spokeswoman Commander Rebecca Rebarich said on Saturday: “We stand by where we said the aircraft was operating in international airspace.”Iran’s Foreign Ministry summoned a diplomatic representative of the United Arab Emirates on Saturday because the UAE allowed the drone that was shot down to be launched from a US military base on its territory, the Fars News Agency reported.Tensions in the region began to worsen significantly when Trump pulled out of a 2015 nuclear deal between Iran and six powers last year and reimposed sanctions on the country. The sanctions had been lifted under the pact in return for Tehran curbing its nuclear program.Over the past weeks, the United States and Iran’s main regional rival, Saudi Arabia, have also blamed Iran for attacks on two oil tankers last week in the Gulf of Oman and on four tankers off the United Arab Emirates on May 12.Both incidents happened near the strategic Strait of Hormuz, a major conduit for global oil supplies.Iran has denied any involvement in those incidents, but world powers are calling for calm and sending in envoys for talks to try to lower the temperature of a dispute that is already helping push up the price of oil.A senior Arab diplomat said the sharply increased tensions would further harm the crisis-hit Middle East region.“Confrontation, whatever we think about Trump or Iran, will be disastrous for everyone,” the diplomat told Reuters on condition of anonymity.The US Federal Aviation Administration on Thursday issued an emergency order prohibiting US operators from flying in an oversea area of Tehran-controlled airspace over the Strait of Hormuz and Gulf of Oman. Some other international airlines are taking related precautions.But Iran said on Saturday its airspace was “safe and secure” for all planes to cross, Tasnim reported.German Chancellor Angela Merkel called on Saturday for a political resolution of the crisis, adding, “That is what we are working on.”Britain’s Foreign Office said Middle East Minister Andrew Murrison would raise concerns about “Iran’s regional conduct and its threat to cease complying with the nuclear deal” during a visit to Tehran on Sunday. France sent an envoy to Iran earlier in the week.Iran has threatened to breach the deal if the European signatories to the agreement fail to salvage it by shielding Tehran from US sanctions.“The Europeans will not be given more time beyond July 8 to save the deal,” Mousavi said, referring to Iran’s deadline of 60 days that it announced in May.Separately, Iran has executed a former contract employee for the aerospace organization of the Ministry of Defense on charges of spying for the CIA, the IRIB news agency reported on Saturday.Jalal Hajizavar had left his post nine years ago and was convicted by a military court after an investigation which discovered documents and spying equipment at his home, the report said.