China is ramping up support for Putin's war in Ukraine by supplying tank components, rocket fuel and other equipment

China has increased its support for Vladimir Putin's war in Ukraine by sending military equipment to Russia, American officials have said.

The alarm was sounded as the Kremlin's Foreign Minister Sergei Lavrov arrived in China for an official visit on Monday, his ministry said, with the two countries looking to strengthen diplomatic ties as Russia's invasion of Ukraine grinds on.

US officials anonymously told Bloomberg that Beijing has sent rifle scopes, tank components, rocket fuel and satellite images to Russia.

They also said that China was providing 'geospatial intelligence' to Moscow to help in its war in Ukraine, as well as sending propellants used in missile production, microelectronics and turbojet engines - bypassing Western sanctions on Russia.

The publication added that it had been told US secretary of state Anthony Blinken had briefed European allies this week on China's ramped-up support.

Putin has regularly courted Chinese support since before he launched the invasion of Ukraine on February 24, 2022.

Western nations regularly urge Beijing to play a greater role in restoring peace in Ukraine by using its influence over the Kremlin. 

While China sees itself as a neutral party in the Ukraine conflict, it has become Russia's leading trade partner in the last two years and favours a political settlement to end the fighting - offering a lifeline to Russia's economy in the face of sanctions.

However, it has appeared reluctant to actively prop up the Russian president's armies who suffered a series of defeats in the first year of the war.

With Moscow's forces now making gains in the east of Ukraine, this appears to have changed - based on the briefing from US officials. 

With Putin's forces out-gunning Kyiv's armies, Russian forces are on the offensive.

Ukraine warned on Friday that a key frontline town was coming under 'constant fire' from advancing troops as Moscow said it had captured another small village. 

The Ukrainian town of Chasiv Yar in the eastern Donetsk region appears to be their next major target. Both Ukrainian and Russian military bloggers with links to the armed forces said Friday that Russian troops had reached the outskirts of the town.

While Ukraine struggles for ammunition - Republican House Speaker Mike Johnson has held up a bill for months that would supply $60 billion in military and financial aid for Kyiv - Russia has switched its economy to a war footing.

Consumer-based factories have been switched to arms manufacturers, and Russia has signed deals with Iran and North Korea for supplies of shells and drones.

This, combined with a greater number of troops, has seen Russia recently secure its first territorial gains since seizing Bakhmut - and it is now trying to press onwards against Ukrainian units hobbled by the delays to vital Western military aid.

With China backing Russia's military, western support would become even more vital in Ukraine's efforts to repel the invaders.

Meanwhile, China's foreign ministry announced long-time Putin ally Lavrov had touched down in Beijing in a post on X (formerly Twitter) on Monday morning.

He will spend two days in the Chinese capital and hold meetings with his Chinese counterpart Wang Yi, according to a previous readout from the ministry.

'An in-depth exchange of points of view is expected on a certain number of 'burning subjects',' the statement said, citing 'the Ukrainian crisis and the situation in the Asia-Pacific region'.

The ministry added that the two men would 'discuss a wide range of questions linked to bilateral cooperation, as well as cooperation on the international scene'.

Lavrov last visited Beijing in October for an international forum on Chinese President Xi Jinping's flagship Belt and Road infrastructure initiative.

It was reported last month that Putin will travel to China in May for talks with Chinese President Xi Jinping, in what could be the Kremlin chief's first overseas trip of his new presidential term - which began with his reelection in March.

Moscow and Beijing declared a 'no limits' partnership in February 2022 when Putin visited Beijing just days before Russia launched its full-scale invasion of Ukraine, triggering the deadliest land war in Europe since World War Two.

US Treasury Secretary Janet Yellen warned Saturday of consequences if Chinese businesses were found to support Russia in the Ukraine war, days after Washington expressed concern Beijing was helping Russia to rebuild its military defence base.

'Secretary Yellen emphasized that companies, including those in the PRC, must not provide material support for Russia's war against Ukraine, including support to the Russian defense industrial base, and the significant consequences if they do so,' the US Treasury said in a statement, referring to the People's Republic of China.

Xi, in a call with Putin last month, said both sides should resolutely oppose interference in domestic affairs by external forces, an apparent reference to the United States.

Chinese vice foreign minister Sun Weidong said bilateral ties were 'at their best in history' when he met his Russian counterpart in Moscow last month, according to a Chinese foreign ministry readout.