Donald Trump and Vladimir Putin are to hold talks on Syria later when they speak for the first time since the US President ordered a missile strike on the country.
Last month's American attack on a Syrian government airbase from where a deadly chemical attack was allegedly launched, strained relations between Washington and Moscow.
The US held the Damascus regime responsible for the atrocity, which Russia sided with their Syrian allies in blaming on rebel forces.
Mr Putin condemned America's military response as a "violation of international law", while Washington said ties had reached a "low point" , amid Moscow's continued support for President Bashar al Assad's regime.
:: Charities struggling to help injured Syrian children
The chemical attack on the rebel-held town of Khan Sheikhoun on 4 April, which UK tests showed to be sarin gas, left more than 80 people dead, many of them children.
In response, the US leader gave orders to fire 59 cruise missiles at the Sharyat military base, southeast of Homs.
The phone call between Mr Trump and Mr Putin will offer the chance to repair recent damage to diplomatic relations.
It will be the third time the two world leaders have spoken since Mr Trump became US president.
In January, they discussed defeating Islamic State when Russia's leader called to congratulate the Republican tycoon on winning the White House.
Mr Trump also offered condolences and support in the wake of the St Petersburg metro suicide bombing that killed 15 people on 3 April.
The UNHCR estimates 4.9 million Syrians have become refugees during the six-year conflict, with many more displaced inside the country.
In the latest fighting, US-backed Syrian fighters say they have made more gains in their battle to take the strategically important city of Tabqa from IS control.
The latest talks between the two leaders come as official investigations continue into links between the US administration and Russia.
The FBI is examining any ties between Mr Trump's campaign associates and the Kremlin, while the Pentagon is carrying out an inquiry into his former national security adviser, Michael Flynn, over payments received from Russian government-linked firms.
US intelligence agencies said hackers directed by Moscow accessed the Democratic National Committee networks ahead of the election that put Trump in the White House.
German Chancellor Angela Merkel has arrived in the Black Sea resort of Sochi for talks with Mr Putin, with the unresolved conflict in Ukraine and Syria's bloody civil war high on the agenda.
Mrs Merkel's one-day visit is her first trip to Russia in two years.
:: Watch Tuesday's special on Syria's forgotten children on Sky News at 8.30pm