Boris Johnson has urged the Turkish president to halt military operations against Syrian Kurds, as the major European powers began efforts to end the conflict.

The prime minister told Recep Tayyip Erdoğan of his “grave concern” at the attacks in northern Syria in a phone call on Saturday, after Germany and France announced that they had suspended all arms exports to Turkey.

“He expressed the UK’s grave concern about Turkey’s military operation in northern Syria, which he said could further worsen the humanitarian situation there and undermine the progress made against Daesh (so-called Islamic State),” a No 10 spokesman said.

“The prime minister underlined that Turkey is an important partner for the UK and a Nato ally. He recognised Turkey’s role at the forefront of the fight against [Isis] and its generosity in supporting refugees who’ve fled the civil war in Syria.

Kurdish forces in Syria will no longer prioritise guarding Isis prisons Read more

“But the prime minister was clear that the UK cannot support Turkey’s military action. He urged the president to end the operation and enter into dialogue, and said the UK and international partners stand ready to support negotiations towards a ceasefire.”

Since the attacks began last Wednesday, aid agencies estimate that 100,000 people have already fled their homes near the Turkey-Syria border. Some reports estimate that between 20 and 40 people had been killed, fighters and civilians and another suggests five Islamic State suspects have escaped from prison in Qamishli after Turkish shelling. Hundreds more Isis suspects are being guarded by Kurdish forces.

Facebook Twitter Pinterest Kurds in Greece protest outside Turkish embassy in Athens. Several European cities saw protests. Photograph: Yannis Kolesidis/EPA

Several European cities saw protests against the attacks on Saturday, as Germany’s foreign minister said the country was suspending arms sales to Erdoğan’s forces. “Against the background of the Turkish military offensive in northeastern Syria, the government will not issue any new permissions for any weapons that can be used by Turkey in Syria,” Heiko Maas told Bild am Sonntag on Saturday. Germany is one of Turkey’s main suppliers of weapons.

Hours later, France’s defence and foreign ministries made an announcement stating their opposition to the Turkish military operation, and said they too had suspended all planned exports of “war materials” to Turkey.

The EU’s foreign affairs committee will meet in Luxembourg tomorrow to decide a co-ordinated, “Europe-wide” approach, the French ministries said.

Finland, Norway and The Netherlands have already announced that they are stopping arms exports to the country. Since the failed coup against Erdoğan in July 2016, the UK has approved £723m of arms exports to Turkey, according to the Campaign Against Arms Trade.

Facebook Twitter Pinterest Turkey-backed Syrian rebel fighters near the border town of Tel Abyad, Syria. Photograph: Khalil Ashawi/Reuters

Erdoğan has justified the attacks as an attempt to remove a terrorist threat posed by elements of the Kurdish-led Syrian Democratic Forces, which led the fight against Isis with the help of military personnel from the US, during which operations it lost 11,000 fighters. The attacks began after Donald Trump pulled US forces out of the area last week.

Earlier, Dominic Raab, the foreign secretary, faced criticism from a Turkish representative at the Nato Parliamentary Assembly in London on Saturday, after he said Turkey should show “maximum restraint”.

The Turkish member told him that Turkey’s operation was “not an invasion” but a “counter-terror operation” but Raab replied: “I just don’t agree. The risk is with the counter-terrorism operation you describe, taking on the SDF (Syrian Democratic Forces) and the broader objectives, is that it is weakening the overarching counter-terrorism goal of countering Daesh.”