LONDON/MOSCOW (Reuters) - U.S. Secretary of State John Kerry said on Tuesday the United States and Russia have planned "concrete steps" for the direction they will take in Syria.

He also urged Russia to use its influence on Syrian President Bashar al-Assad to halt Syrian military attacks on opposition groups and civilians.

Kerry spoke to Russian Foreign Minister Sergei Lavrov by phone earlier on Tuesday and discussed ways to resolve the Syria crisis, the Russian Foreign Ministry said in a statement.

At a news conference in London, Kerry said he would update his fellow foreign ministers at an international meeting on Syria in the British capital on Tuesday, describing his visit to Moscow last week "and the concrete steps that the U.S. and Russia are planning to take."

"I spoke to Foreign Minister Lavrov again today," he said.

"We both believe that we have an understanding of the direction we are going in and what needs to be achieved and our teams will meet shortly and we are going to continue to do that in order to bolster the cessation of hostilities and in order to increase our capacity to fight back against al Qaeda, which is Nusra, as well as fight back against ISIL," Kerry said.

"We will also do everything in our power to improve delivery of food, medicine, water, incredibly essential humanitarian needs," Kerry said.

In a meeting with U.N. Syria envoy Staffan de Mistura in London, Kerry said it was vital for Moscow to use its influence with the Assad regime to halt its attacks on opposition groups and innocent civilians, which he said were in violation of the cessation of hostilities.

He also emphasized the need to end all attempts to besiege the city of Aleppo and other besieged towns and ensure full humanitarian access there, according to State Department Spokesperson John Kirby.

Kerry said last week after talks with President Vladimir Putin and Lavrov in Moscow he had reached a common understanding on the steps needed to get Syria's peace process back on track.

However he declined to give details and said that more work was needed before those steps could be implemented and that Russia and the United States still differed over the future of Syrian President Bashar al-Assad.

At the same London news conference, Britain's Foreign Secretary Boris Johnson called on Russia to use its "unique ability" to stop the Syrian conflict by convincing Assad to put an end to five years of fighting that have ravaged the country.

"Russia in particular has a unique ability to persuade the Assad regime to end the carnage and return to the negotiating table," Johnson said.

Johnson called the current Syrian situation "dire" and said the country faced a "terrible humanitarian catastrophe".

Russia backs Assad and is giving military help to his campaign against rebel fighters. The United States believes the Syrian leader has to go and is supporting some of the rebel groups who are fighting to unseat him.

The Washington Post newspaper reported last week that Kerry went to Moscow with a proposal for intelligence sharing with Russia over Syria and joint selection of bombing targets.

A Kremlin spokesman said last week that Putin and Kerry had not directly discussed military cooperation.

The Russian Foreign Ministry said Kerry and Lavrov also discussed Russia's doping scandal.

"Lavrov told Kerry all that he thinks about the anti-Russian, inflammatory claims made by the U.S. Anti-Doping agency to the International Olympic Committee," it said.

(Reporting by Vladimir Soldatkin in Moscow and David Brunnstrom in London; Editing by Jack Stubbs)