The push to impose new sanctions on Russia following the deadly chemical weapons attack in Syria has hit trouble amid claims that the EU and Germany are “cool” on the idea.

Sources at the G7 in Italy told The Independent that Britain and America’s plan for new punitive measures on Moscow are being taken seriously, but face hurdles before receiving international approval.

To win backing, Foreign Secretary Boris Johnson may have to narrow the measures’ scope and already accepts none will be imposed before the completion of an investigation into the chemical incident at the village of Khan Sheikhoun last week.

In a bid to give the plan force Theresa May and Donald Trump spoke on the phone on Monday night and agreed there is now a “window of opportunity” for Russia to ditch its support for the Syrian regime of Bashar Assad.

Sources at the G7 said: “The UK and the US are pushing but the Germans and the EU representative are cool on the idea.

“The sanctions are still on the table, but they know they will have to wait until the investigation into the chemical weapons attack before they can be implemented.

“Several people have referred to sanctions here so the US and UK are not isolated, but it’s not universal at this stage.”

US Secretary of State Rex Tillerson is travelling to Moscow imminently and had hoped to take with him a definite statement of intent from the G7 nations and other partners, including Middle Eastern allies who are at the Lucca meeting.

In pictures: US missile strike against Syria Show all 7 1 /7 In pictures: US missile strike against Syria In pictures: US missile strike against Syria The guided-missile destroyer USS Porter (DDG 78) launches a tomahawk land attack missile in the Mediterranean Sea AP In pictures: US missile strike against Syria The United States military launched at least 50 tomahawk cruise missiles at al-Shayrat military airfield near Homs, Syria, in response to the Syrian military's alleged use of chemical weapons in an airstrike in a rebel held area in Idlib province EPA In pictures: US missile strike against Syria Shayrat airfield in Syria Getty Images In pictures: US missile strike against Syria US Navy guided-missile destroyer USS Ross (DDG 71) fires a tomahawk land attack missile in Mediterranean Sea Reuters In pictures: US missile strike against Syria US Navy guided-missile destroyer USS Ross (DDG 71) fires a tomahawk land attack missile in Mediterranean Sea Reuters In pictures: US missile strike against Syria President Donald Trump speaks at Mar-a-Lago in Palm Beach, Fla., after the US fired a barrage of cruise missiles into Syria in retaliation for this week's gruesome chemical weapons attack against civilians AP In pictures: US missile strike against Syria Syria's President Bashar al-Assad Reuters

But with just hours left to negotiate it was unclear how solid his backing for new sanctions would be going into the meeting with Vladimir Putin’s representatives.

A source at the EU told The Independent any sanctions by the block would need the unanimous support of member states, adding: “There are clear procedures for sanctions at EU level.”

The White House said Mr Trump had called Angela Merkel to discuss Syria. But while officials said the German leader "expressed support" for the US military action and agreed on the importance of holding Assad "accountable", there was no mention of sanctions.

A spokesman said: "President Trump and his counterparts agreed to stay in touch regarding Syria and other international issues of mutual concern."

Even Canada, one of the closest allies of the UK and US, would only say it was exploring the idea of new sanctions on Tuesday.

With wrangling still going on over the issue, Mr Trump thanked Ms May on the phone for her support in the wake of last week's US missile attack on the air base from which the chemical attack is believed to have been launched.

A Downing Street spokesman said: “The Prime Minister and the President agreed that a window of opportunity now exists in which to persuade Russia that its alliance with Assad is no longer in its strategic interest.

Russia and Iran have threatened the US over Syria

“They agreed that US Secretary of State Tillerson's visit to Moscow this week provides an opportunity to make progress towards a solution which will deliver a lasting political settlement.”

There was outrage across the world after dozens of civilians were killed in what is believed by the West to have been a chemical weapons attack by the Assad regime.

Anticipating tough language from the G7 in Italy, Russia and Iran issued on Monday a joint call for an “unbiased investigation” into the gassing at the Syrian village.