In a surprising move, the US has postponed the \u20182+2 dialogue', for which External Affairs Minister Sushma Swaraj and Defence Minister Nirmala Sitharaman were scheduled to travel to Washington on July 6. The dialogue was put off due to \u201cunavoidable reasons\u201d, said Ministry of External Affairs spokesperson Raveesh Kumar on Wednesday. Swaraj and Sitharaman were slated to meet US Secretary of State Mike Pompeo and Secretary of Defence James Mattis. The dialogue has been seen as a vehicle to elevate the strategic relationship between the two countries. The meeting was expected to focus on strengthening strategic, security, and defence cooperation. \u201cUS @SecPompeo spoke to EAM @SushmaSwaraj a short while ago to express his regret and deep disappointment at the US having to postpone the 2+2 Dialogue for unavoidable reasons,\u201d Ministry of External Affairs Spokesperson Raveesh Kumar tweeted. \u201cUS @SecPompeo sought EAM @SushmaSwaraj understanding, and they agreed to identify new mutually convenient dates to hold the Dialogue at the earliest, in India or the US. 2\/2,\u201d he posted on Twitter. Series of delays: This new dialogue format was agreed upon between the two sides during the visit of Prime Minister Narendra Modi to Washington in June 2017. After June last year, the two countries have tried to schedule the dialogue many times with several dates having been considered. Earlier this year also, the '2+2 dialogue' had been postponed due to uncertainty over the confirmation of Pompeo as President Donald Trump's new Secretary of State. Pompeo was later confirmed as Secretary of State in April. Reports also say Donald Trump may meet Vladimir Putin in July and Pompeo will be busy in visiting some key countries. The schedule for 2+2 dialogue was coinciding with Pompeo's visits. Russia, Iran the bones of contention? The postponement came after New Delhi showed its keen interest in purchasing the S-400 missile system from Russia. This comes in the backdrop of a debate over a legislation against Russian defence entities in the US Congress. The legislation, if passed could cover the nations buying defence and other gadgets under its ambit. Notably, the Countering America\u2019s Adversaries through Sanctions Act (CAATSA), which is considered as a measure to clamp down against \u201coligarchs\u201d close to President Vladimir Putin\u2019s government, also targets the equipment like Russian S-400 missile system. New Delhi's ties with Tehran: Apart from Russia, reports say that the postponement may also have happened due to India's business dealings, chiefly oil, with Iran. Trump administration has categorically asked New Delhi and Being to cut all imports of Iranian oil by November 4. Iran is India's third-largest oil supplier behind Iraq and Saudi Arabia. Iran supplied 18.4 million tonnes of crude oil during April 2017 and January 2018, according to a PTI report. Plausible impact: The postponement of the maiden 2+2 dialogue between Washington and New Delhi assumes grave significance as American experts were hoping that the dialogue will help change the current narrative surrounding the bilateral relationship amid trade issues between the two countries.