GENEVA (Reuters) - U.S. President Donald Trump’s national security adviser John Bolton said on Thursday he had warned Moscow against meddling in the U.S. midterm elections in November during talks with the head of Russia’s National Security Council.

Bolton said he had also raised with Nikolai Patrushev the issue of tightening economic sanctions against Iran and said they had discussed a phased withdrawal of Iran’s presence in Syria, but gave no details.

“I made it clear we wouldn’t tolerate (election) meddling in 2018 and that we were prepared to take necessary steps to prevent it from happening,” Bolton told a news conference after more than five hours of talks with Patrushev in Geneva.

The United States has already imposed economic sanctions against Russia over its alleged meddling in the 2016 U.S. presidential election. Moscow denies the allegations.

Bolton said differences over the alleged meddling had prevented the two sides from issuing a joint final statement after the first high-level meeting of its kind since Trump met President Vladimir Putin in Helsinki in July.

In answer to a question, Bolton said that he had not raised the statement by Microsoft Corp on Monday that hackers linked to Russia’s government had sought to launch cyber attacks on U.S. political groups. He noted Microsoft was not a U.S. governmental institution.

LINES OF COMMUNICATION

“I think we made a lot of progress, we identified certain areas where lines of communication could be restored and more work done by the affected agencies - State Dept, Defense Department, other agencies as well,” Bolton said.

Patrushev was quoted by Russian news agencies as saying they had broadly agreed to re-open communication lines between their respective foreign and defense ministries.

Bolton, one of the Trump administration’s leading hawks in dealing with Iran’s nuclear program, held talks with Israel’s Prime Minister Benjamin Netanyahu in Jerusalem this week.

Bolton said on Thursday that following the U.S. decision to withdraw from a 2015 international deal aimed at curbing Tehran’s nuclear program, the Trump administration’s objective was to “put maximum pressure on the regime” by making sanctions “more extensive and more effective”.

Patrushev had not sought Russian waivers on sanctions during their talks, he added.

Commenting on Iran’s role in Syria’s long-running conflict, Bolton said: “Our objective is that all Iranian forces return to Iran ... And we talked about a variety of ways in which it might be accomplished through a series of steps.”

Bolton, a critic of the New START treaty agreed during Democratic President Barack Obama’s administration, said the two sides did not set a date for deciding what to do about the treaty due to expire in 2021.

“We are very very early in the process of considering what we are going to do with New START or the INF treaty,” he said, referring to the Intermediate-Range Nuclear Forces pact.