By Samuel Horti in London and James Landale in Munich
BBC News
China is considering giving Russia weapons and ammunition for the Ukraine war, US Secretary of State Antony Blinken has said.
Mr Blinken told CBS News that Chinese companies were already providing "non-lethal support" to Russia - and new information suggested Beijing could provide "lethal support".
This escalation would mean "serious consequences" for China, he warned.
China has denied reports that Moscow has requested military equipment.
Chinese President Xi Jinping is an ally of Russian President Vladimir Putin and is yet to condemn Russia's invasion - but he has sought to remain neutral in the conflict and has called for peace.
China's foreign ministry said it would not accept "finger pointing" and "coercion" from the US over its relations with Russia.
Mr Blinken was speaking to CBS after he met China's top diplomat, Wang Yi, on Saturday at the Munich Security Conference.
He said that during the meeting he expressed "deep concerns" about the "possibility that China will provide lethal material support to Russia".
"To date, we have seen Chinese companies... provide non-lethal support to Russia for use in Ukraine. The concern that we have now is based on information we have that they're considering providing lethal support," he said.
He did not elaborate on what information the US had received about China's potential plans. When pressed on what the US believed China might give to Russia, he said it would be primarily weapons as well as ammunition.
The US has sanctioned a Chinese company for allegedly providing satellite imagery of Ukraine to the mercenary Wagner Group, which supplies Russia with thousands of fighters.
Mr Blinken told CBS that "of course, in China, there's really no distinction between private companies and the state".
What support is China offering Russia?
What weapons are being supplied to Ukraine?
What is Russia's Wagner Group of mercenaries?
If China provided Russia with weapons, that would cause a "serious problem for us and in our relationship", he added.
Relations between Washington and Beijing were already poor after the US shot down an alleged Chinese spy balloon in early February. Both sides exchanged angry words, but equally both sides appeared embarrassed by the incident and seemed ready to move on.
But if China were to deliver weapons to help Russian forces in Ukraine, then US-Chinese relations would deteriorate much more severely.
Mr Blinken's warning seems to be clearly designed to deter China from doing that.
Mr Blinken also said the US was worried about China helping Russia evade Western sanctions designed to cripple Russia's economy. China's trade with Russia has been growing, and it is one of the biggest markets for Russian oil, gas, and coal.
Nato members, including the US, are sending a variety of weapons, ammunition and equipment to Ukraine, including tanks. They have stopped short of sending fighter jets, and Mr Blinken would not be drawn on whether the US would help other countries supply jets.
"We've been very clear that we shouldn't fixate or focus on any particular weapons system," he said.
He did, however, say that the West must ensure Ukraine had what it needed for a potential counter offensive against Russia "in the months ahead". Russia is currently trying to advance in eastern regions of Ukraine, where some of the fiercest fighting of the war has taken place.
Mr Wang said in Munich on Saturday that China had "neither stood by idly nor thrown fuel on the fire" for the Ukraine war, Reuters reported.
قال وانغ إن الصين ستنشر وثيقة توضح موقفها من تسوية النزاع. وقال إن الوثيقة ستنص على وجوب احترام وحدة أراضي جميع الدول.
وقال وانغ: "أقترح أن يبدأ الجميع في التفكير بهدوء ، وخاصة الأصدقاء في أوروبا ، بشأن نوع الجهود التي يمكننا بذلها لوقف هذه الحرب".
وأضاف أن هناك "بعض القوى التي يبدو أنها لا تريد أن تنجح المفاوضات أو تنتهي الحرب قريباً" ، لكنه لم يذكر من يقصد.
من المقرر أن يلقي الرئيس الصيني ، السيد شي ، "خطاب سلام" في ذكرى الغزو الروسي لأوكرانيا يوم الجمعة ، 24 فبراير ، وفقًا لوزير الخارجية الإيطالي أنطونيو تاجاني.
وقال تاجاني للإذاعة الإيطالية إن خطاب شي سيدعو إلى السلام دون إدانة روسيا ، حسبما ذكرت رويترز.
خلال اجتماعهما ، تبادل السيد بلينكين والسيد وانغ أيضًا كلمات قوية حول الخلاف المتعمق حول بالون تجسس صيني مزعوم تم إسقاطه فوق الولايات المتحدة.
وقال السيد بلينكين خلال الاجتماع إن الولايات المتحدة "لن تقف مع أي انتهاك لسيادتنا" ، وقال "هذا العمل غير المسؤول يجب ألا يحدث مرة أخرى أبدًا".
وقال السيد بلينكين لشبكة سي بي إس إن الدول الأخرى كانت قلقة بشأن ما أسماه "برنامج بالون المراقبة" الصيني عبر القارات الخمس.
في غضون ذلك ، وصف وانغ الحلقة بأنها "مهزلة سياسية من صنع الولايات المتحدة" واتهمها "باستخدام كل الوسائل لعرقلة وقمع الصين". نفت الصين إرسال بالون تجسس.
وصباح الأحد ، حذرت بكين من أن الولايات المتحدة "ستتحمل كل العواقب" إذا صعدت الجدل حول البالون. وقالت وزارة الخارجية في بيان لوزارة الخارجية نقلته رويترز إن الصين "ستتابع حتى النهاية" في حالة "إصرار الولايات المتحدة على استغلال القضية".
ومن المقرر بث المقابلة الكاملة مع شبكة سي بي إس - الشريك الإذاعي لبي بي سي في الولايات المتحدة - يوم الأحد.