Egypt has flatly rejected a warning by the European Union that it will "urgently review" its aid to the country against a background of mounting international concern about the deteriorating situation and the huge loss of life in the last few days.

Nabil Fahmy, foreign minister in the military-backed interim government, warned on Sunday against the "internationalisation" of a crisis he described as Egypt's internal affair and criticised the "silence" of foreigners on attacks he blamed on the Muslim Brotherhood.

Reflecting a defiant official mood in Cairo, Fahmy ignored a public statement by the British foreign secretary, William Hague, who sought to strike a careful balance by condemning the "disproportionate use of force by the security forces or violent actions by some demonstrators". The statement was issued after the two men spoke on Saturday night, the Foreign Office said.

Diplomats said that Egypt was furious at last week's British and French calls for a private UN security council debate on the escalating crisis. Ban ki-Moon, the secretary-general, has expressed his concern and is sending a senior UN official to Cairo. More than 800 people, mostly Brotherhood supporters, were killed last week in the worst violence since President Mohamed Morsi was deposed in early July.

State media reported on Sunday night that 38 Brotherhood members taken prisoner had been killed in a riot. The pro-Morsi anti-coup alliance said it had evidence the detainees had been "assassinated" in a truck taking them to Abu Zaabal prison in northern Egypt.

Al-Jazeera TV said the men had been arrested in the evacuation of Cairo's al-Fath mosque on Saturday. The detainees were part of a prison truck convoy of some 600 people heading to Abu Zaabal, officials told Associated Press.

Detainees in one truck managed to capture a police officer, officials told AP. Security forces fired tear gas into the truck in hopes of freeing the badly beaten officer, the officials said. The officials said those killed died from the effects of the gas.

Members of the student wing of Islamic party Jamaat-e-Islami demonstrate in support of Egypt’s Mohamed Morsi in Karachi. Photograph: Asif Hassan/AFP

Sunday's state TV broadcasts – tagged with an "Egypt fighting terrorism" logo – ran repeated interviews with citizens agreeing with the government's rejection of foreign involvement.

EU foreign ministers are expected to meet in Brussels this week to discuss Egypt after the presidents of the European council and European commission, Herman Van Rompuy and José Manuel Barroso, warned jointly on Sunday that further escalation could have "unpredictable consequences". The EU had pledged almost €5bn (£4.2bn) in loans and grants for 2012-2013.

In a statement they said the EU would "urgently review in the coming days its relations with Egypt".

"We regret deeply that international efforts and proposals for building bridges and establishing an inclusive political process ... were set aside and a course of confrontation was instead pursued," they added.

But Fahmy suggested bluntly that Cairo could manage without EU help. "I want to determine what is useful and what is not and what aid is being used to pressure Egypt and whether this aid has good intentions and credibility," he told reporters in Cairo. "We are not looking to replace one friend with another but we will look out to the world and continue to establish relations with other countries so we have options."

Relations between Egypt and the US have been strained by the crisis, but President Barack Obama has faced criticism for merely suspending the two countries' annual Bright Star joint military exercise but not touching $1.5bn (£959m) in annual aid to the Egyptian armed forces. On Sunday, Obama's former presidential rival and influential Republican foreign policy voice John McCain said Obama's failure to follow through on a threat to cut off aid if there was a coup in Egypt, meant the administration was "not sticking to our values".

But Fahmy said: "The relationship between Egypt and the US has been there for a long time. It has been through ups and downs in the past. We hope things will go back to normal promptly."

Tamarod (Rebellion), the movement that organised the 30 June mass protests that ended with Morsi's removal by the army, said on Sundayit was launching a petition calling for an end to all US assistance to Egypt and the abrogation of its 1979 peace treaty with Israel, the linchpin of US strategy in the region. It cited "unacceptable American intervention in Egyptian affairs and US support for "terrorist groups".

In the face of western criticism, Egypt is now relying increasingly on political and financial support from its conservative Arab allies, led by Saudi Arabia and the United Arab Emirates, sworn enemies of Morsi and the Brotherhood and the leaders of the counter-revolutionary response to the uprisings of the Arab spring. Al-Akhbar, a leading state-run newspaper, on Sunday published a cartoon of an avuncular-looking King Abdullah of Saudi Arabia extending generous cash support to an Egyptian.

Fahmy told Hague and other foreign ministers that "the Brotherhood and its allies were terrorising citizens, attacking governmental institutions, hospitals, churches, places of worship [and] causing … a threat to domestic peace and security". The Egyptian minister also criticised the international community. "Their silence encourages armed groups to continue murdering and using violence and intimidation," he said.

The responsibility of any government was to provide security and impose public order within the context of the law, Al-Ahram reported.