London (AFP) - The US has lost its role as mediator in the Middle East by moving its embassy in Israel to Jerusalem, Turkish President Recep Tayyip Erdogan said in London on Monday.

"With its latest step, America has chosen to be a part of the problem, not a solution, and lost its mediator role in the Middle East peace process," Erdogan told the Chatham House international affairs think-tank.

Moving the embassy from Tel Aviv to Jerusalem was "very, very unfortunate", he said, warning it would "increase tensions and ignite an even greater fire between communities".

His remarks came as violent clashes erupted along Gaza's border ahead of the controversial embassy opening, leaving dozens of Palestinians dead and hundreds wounded in the conflict's bloodiest day in years.

Erdogan urged the international community to "take swift action to put an end to Israel's increasing aggression", denouncing the embassy move as violating international law and United Nations resolutions.

Jerusalem is one of the most thorny issues of the Israeli-Palestinian conflict, with both sides claiming it as their capital.

Most of the international community does not formally recognise Jerusalem as Israel's capital, and almost all embassies are located in Tel Aviv.

"The establishment of an independent Palestinian state with Jerusalem as its capital is the only way for lasting peace and stability," the Turkish leader said.

- Red carpet for Erdogan -

Erdogan was also deeply critical of US President Donald Trump's decision to withdraw Washington from the Iran nuclear deal.

"The nuclear deal is a significant development which should be preserved," Erdogan said, adding that political dialogue with Iran was "beneficial" to the international community.

Turning to Turkey's decades-long efforts to join the European Union, Erdogan said it remained a strategic goal for Ankara but he condemned the "politicisation" of the process.

Erdogan began a three-day visit to Britain on Sunday, with London rolling out the red carpet as it seeks to bolster future trade ties after leaving the EU next year.

Story continues

On Tuesday he will meet British Prime Minister Theresa May.

The meeting is "an opportunity for the UK and Turkey to build on our close cooperation on counter-terrorism, migration, regional stability and in other vital areas," her spokesman said.

"Our close relationship with Turkey allows us to have frank discussion and you can expect that the prime minister will raise human rights.

"We want Turkey to uphold its international obligations, including respect for freedom of expression and political freedoms."

Erdogan will meet also Queen Elizabeth II on Tuesday.

As he spoke at Chatham House, a group of Kurdish activists protested outside, with further demonstrations expected near Downing Street on Tuesday by media rights group, Reporters Without Borders.

Erdogan's visit comes just weeks before Turkey holds early parliamentary and presidential elections on June 24.

Erdogan, who has dominated Turkey's political scene for the past 15 years, is seeking to reinforce his authority as Turkey moves to a new presidential system of government with expanded powers.

Earlier on Monday, he met three footballers from Turkey or of Turkish origin who play in the English Premier League -- Cenk Tosun, Mesut Ozil and Ilkay Gundogan, state-run news agency Anadolu reported.