Protest group Tāmaki for Palestine has claimed responsibility for red paint splashed on the doors of MFAT and the US Consulate's Auckland buildings this morning, saying the move was to "make the blood on US and New Zealand officials' hands visible".
One person has been arrested, a police spokesperson said.
"This paint represents the thousands of Palestinian men, women and children killed by Israel over the past 37 days and before," a statement from the group said.
Alongside the red paint, messages calling for a ceasefire could be seen.
Since Hamas' surprise October 7 attack, Israel's retaliation has seen more than 11,000 Palestinians die according to the Health Ministry in Gaza, which does not differentiate between civilian and militant deaths.
At least 1200 people have died on the Israeli side, mostly civilians killed in the initial Hamas attack.
"This didn't start on October 7. The USA has propped up the Israeli occupation of Palestine since 1948," Tāmaki for Palestine said, also pointing to current US military aid for Israel. "It needs to end.
"It's clear that the USA is complicit and abetting the Israeli genocide against Palestinians in Gaza."
An embassy spokesperson said the US is focused on addressing the humanitarian needs of civilians in need.
"The United States supports the right of people to voice their opinion through peaceful protest, but civil protests do not include vandalising property," the spokesperson said.
"As we stand with the people and government of Israel, we also stand with Palestinian civilians."
The New Zealand government's response to the conflict also came in for criticism from Tāmaki for Palestine.
"We have yet to condemn Israel or the US's actions, or impose sanctions (as we did towards Russia at the outset of the conflict in Ukraine)," the protest group said.
"Tāmaki for Palestine demands the New Zealand Government use its diplomatic influence to support an immediate Israeli ceasefire.
"This includes ending diplomatic ties with the USA to pressure said imperialist superpower to also support an immediate Israeli ceasefire."
Police are aware of the incidents, a spokesperson said.
"Police were called following a report of vandalism on a building on Quay Street at around 1.50am, and shortly after also located further graffiti at a building on Customs Street.
"One person was arrested and at this stage, our enquiries are in the very early stages to determine the full circumstances."
Anyone with information is asked to call 105 and reference event number P056717234.
Tāmaki for Palestine also called for "the incoming New Zealand Government [to] publicly declare support for an immediate Israeli ceasefire and recognise the State of Palestine".
It comes after New Zealand last month voted for a UN resolution for a humanitarian truce between Gaza and Israel.
Premier House, the official residence of the prime minister in Wellington, was also vandalised overnight.
Nobody has claimed responsibility for the messages on the fence there at this stage.
"Police are making inquiries following a report of graffiti outside Premier House," a police spokesperson said.
"Our inquiries are in the very early stages to determine the full circumstances."
Anyone with information is urged to call 105 and reference event number P056718261.
Foreign Minister Grant Robertson said: "We reject the vandalism that occurred overnight. While we understand that emotions are running high for many in our community, we urge everyone to act legally, respectfully and peacefully."
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