US Secretary of State John Kerry says in a letter on 2 September designed to reassure critics of the Iran nuclear deal that the US will intensify its defence and security support of Israel and the GCC.

The letter was sent ahead of the end of US congress’ summer recess on 8 September which will be followed by votes in the House of Representatives and the Senate disapproving the Joint Comprehensive Plan of Action (JCPOA) agreed on 14 July. They are expected to vote against the JCPOA  but will fail to muster the two-thirds’ majorities in both required to override a subsequent veto by President Obama. It was announced on 2 September that 34 senators had expressed support for the deal, sufficient to uphold President Obama’s veto.

“We share the concern expressed by many in Congress regarding Iran’s continued support for terrorist and proxy groups throughout the region, its propping up of the Asad regime in Syria, its efforts to undermine the stability of its regional neighbours, and the threat it poses to Israel,” Kerry’s letter says. “We have no illusion that this behaviour will change following implementation of the JCPOA. That is precisely why we have been so focused on preventing Iran from acquiring a nuclear weapon – because it stands to common sense that any country with a nuclear weapon presents a different challenge than a country without one.”

The letter says President Obama views Israel’s security as sacrosanct and has increased US military, intelligence, and security cooperation with Israel to their highest levels ever.

The US is expanding defence cooperation with the GCC which has included $129 billion in authorised sales of advanced military systems since 2009. The departments of state and defense have created working groups to strengthen security cooperation the GCC,” the letter says.

“As part of this effort, our arms transfer working group is working to expedite the delivery of capabilities needed to deter and combat regional threats, including terrorism and Iran’s destabilising activities in the region,” the letter says. In July, the White House notified Congress of major defence sales to Saudi Arabia and the UAE.

Kerry’s letter says the US is building political support for multilateral US-GCC ballistic missile defence (BMD) co-operation as part of plan to deter Iranian aggression against the GCC.

“We have already made significant progress and are working with the GCC to propose a robust BMD early warning architecture to meet our partners’ needs,” the letter says. “As part of our expanded counter-terrorism cooperation, we are increasing our information sharing to ensure we and our GCC partners remain postured effectively to counter new threats.”

Kerry’s letter says he will meet GCC foreign ministers in New York in September to follow up an initial meeting in Doha in August. The US will support action to contain Iran including UN Security Council resolutions banning weapons transfers to Hizbollah, Houthis in Yemen and Shia militants in Iraq as well as transfers involving North Korea.

“We will also continue to use the full range of tools at our disposal to counter Iran’s missile program, including the Missile Technology Control Regime,” the letter says. The US will continue to impose sanctions on Iran to counter missile proliferation after nuclear-related sanctions are lifted and is co-operating with its regional partners to block Iranian “illicit” shipments.