BBC News
Ukraine says it has recaptured ground in Bakhmut, a rare advance after months of grinding Russian gains in the eastern city.
Deputy Defence Minister Hanna Malyar said Ukrainian forces advanced two kilometres (1.2 miles) in a week.
The claims signal a momentum shift in Bakhmut - but more widely, there is no clear evidence of an Ukrainian counter-offensive.
However, two explosions were reported on Friday in Russian-occupied Luhansk.
Images posted on social media, verified by the BBC, show a big plume of black smoke rising from the city, which lies about 90km (55.9 miles) behind the front line in eastern Ukraine.
The cause has not been confirmed - but the blasts come a day after the UK said it had supplied Ukraine with long range Storm Shadow cruise missiles.
Luhansk is beyond the reach of the Himars rockets Ukraine has previously relied on for deep strikes against Russian targets.
Earlier Russia denied reports of Ukrainian gains in Bakhmut, after claims from both sides.
"The individual declarations on Telegram about a 'breakthrough' on several points on the frontline do not correspond to reality," Russia's defence ministry said.
"The general situation in the special military operation zone is under control," it added, using Russia's term for the invasion.
However, in a updated statement on Friday morning the ministry claimed Russian troops had changed their position for strategic reasons.
It said units of the southern group of Russian forces had taken up a better defensive position in the Maloilinivka area, something which took into consideration "the favourable conditions of the Berkhivka reservoir".
Maloilinivka and Berkhivka are both near Bakhmut.
Responding to the statement, the head of Russia's Wagner mercenary group Yevgeny Prigozhin said what the Ministry of Defence was talking about "is unfortunately called 'fleeing' and not a 'regrouping'".
As the intense, bloody battle has worn on, Bakhmut has become symbolically important - though many experts question its tactical value.
In a post on Telegram, Ms Malyar said Bakhmut has become a target of "almost sacred" importance to Russia.
She accused the Kremlin of simultaneously claiming false victories on one hand, while also spreading lies about being short on weapons and ammunition.
Describing the "real situation" over the past week, Ms Malyar claimed Russia suffered significant troop losses, as Ukraine gained 2km without losing any positions.
Earlier Prigozhin accused regular Russian troops of abandoning positions in Bakhmut.
"The situation on the flanks is developing according to the worst predicted scenario," he said.
And Russian military bloggers reported Ukrainian advances or troop movements in several areas.
The Institute for the Study of War also said Ukrainian forces had probably made gains of 2km in Bakhmut.
And the US-based think tank said the Russian defence ministry acknowledging "the Ukrainian counterattacks uncharacteristically quickly" - by denying them - indicated "increased panic".
Meanwhile the BBC has verified video of soldiers with Ukrainian identifying markings posing in front of a gate and a tank in the distance, also with Ukrainian markings.
The video, published on 11 May, has been located to an area around Bakhmut industrial college, until recently held by Wagner troops.
Away from Bakhmut, the exiled mayor of Melitopol reported a large explosion on Friday morning in the centre of the city in south-eastern city, which has been occupied by Russia since the start of the war.
It's not known what caused the blast, but the Ukrainian air force made 14 strikes on Russian forces and military equipment on Thursday, Ukraine's armed forces said.
Alongside the air strikes, Ukraine said it destroyed nine Russian drones and carried out successful attacks on dozens of military targets - including artillery units, an ammunition warehouse and air defence equipment.
After months of stalemate, a Ukrainian counter-offensive - helped by newly-arrived Western weapons - has been openly discussed. But Ukraine's president said on Thursday it was too early to start the attack.
"With [what we already have] we can go forward and, I think, be successful," President Volodymyr Zelensky said in an interview.
"لكننا سنخسر الكثير من الناس. أعتقد أن هذا غير مقبول. لذلك نحن بحاجة إلى الانتظار. ما زلنا بحاجة إلى مزيد من الوقت."
لكن على الرغم من تصريحات الرئيس زيلينسكي ، زعمت مراسلة الحرب الروسية الموالية للكرملين ساشا كوتس أن الهجوم المضاد قد بدأ.
وقال نقلا عن مصادر "موثوقة" إن الدبابات الأوكرانية كانت على طريق خاركيف الدائري متجهة نحو الحدود مع روسيا. لا يمكن التحقق من ادعاءاته بشكل مستقل.
وأضاف كوتس: "توجد رافعات منخفضة في الأعمدة تحمل نماذج [دبابات] غربية من بين نماذج أخرى".
وقال "بعبارة أخرى ، قررت كييف [كييف] تفاقم الوضع على طول الجبهة الشمالية بالتوازي مع بدء العمليات الهجومية على أطراف أرتيوموفسك.
لي لباخموت].
غرفة الحوادث - أوكرانيا: كيف ستنتهي؟
يفكر فرانك جاردنر في النتائج المحتملة للحرب ، حيث تستعد أوكرانيا لهجوم مضاد ضد القوات الروسية.
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كتب مراسل حربي روسي آخر ، ألكسندر سيمونوف ، على Telegram أن القوات الأوكرانية اخترقت بالقرب من قرية Bohdanivka ، بالقرب من Bakhmut ، وأخذت "عدة كيلومترات مربعة" من الأرض.
وقال المحلل العسكري الأوكراني أولكسندر موسيفينكو إن كييف أدركت أن الهجوم المضاد المتوقع قد لا يهزم روسيا بالضرورة "في جميع المناطق المحتلة".
وقال لراديو نيفادا الأوكراني إن هناك احتمالا كبيرا لاستمرار الحرب في العام المقبل. وقال "كل هذا يتوقف على كيفية تطور المعارك. لا يمكننا ضمان كيفية تطور الهجوم المضاد."
قال مسؤول عسكري أمريكي كبير لم يذكر اسمه لشبكة CNN إن القوات الأوكرانية تستعد لهجوم مضاد كبير بضرب أهداف مثل مستودعات الأسلحة ومراكز القيادة وأنظمة الدروع والمدفعية.
كما سبق التقدم الأوكراني في ربيع 2022 في الأجزاء الجنوبية والشمالية الشرقية من البلاد بهجمات جوية "لتشكيل" ساحة المعركة.
قالت وزارة الدفاع الروسية إنها أوقفت العديد من الهجمات الأوكرانية طوال يوم الخميس وقالت إن المعركة الجارية بالقرب من مالينيفكا في شرق دونيتسك تشارك فيها القوات الجوية والمدفعية.
ساهم دانييل بالومبو وريتشارد إيرفين-براون في كتابة هذا المقال