The RAF was forced to abort two attempts to drop aid for Yazidi refugees sheltering on Mount Sinjar in northern Iraq on Sunday night amid fears that the cargo could have injured people on the ground.

The Ministry of Defence (MoD) said the crew of an RAF C130 Hercules aircraft, which had successfully dropped water and solar lanterns on Saturday, had taken the "responsible" decision to abort the mission.

The announcement came as Downing Street brushed off cross-party calls for parliament to be recalled to discuss the Iraqi crisis. Iain Duncan Smith, the work and pensions secretary, declined to be drawn into the discussion about recall, saying it was a matter for the speaker.

"Whether there should be a recall of parliament is not a matter for ministers at this stage," he told the Guardian. "It is up to the speaker, and I, as a member of the government, support the prime minister's position of offering aid," he added.

But the calls from Tory and Labour MPs, who won the support of the former head of the army, Lord Dannatt, are likely to increase after No 10 indicated that Britain may be willing to follow the example of the US in arming Kurdish forces.

The prime minister's spokeswoman said: "Our focus is on the humanitarian effort. We do think it is important that the Iraqi forces, including the Kurdish forces, are able to respond to Isil [Isis] and to tackle this crisis. So we will look at what options there are that might enable them to do that. But there have not been discussions, substantive discussions of that yet. There are certainly no decisions."

Downing Street said Britain's main focus was on providing humanitarian assistance to the Yazidi refugees and putting pressure on Nouri al-Maliki, Iraq's Shia prime minister, to lead a unified government. He has been criticised for divisive leadership that has alienated Sunnis.

Philip Hammond, the foreign secretary who on Monday chaired a meeting of the government's emergency Cobra committee, spoke on Sunday to Masoud Barzani, the president of Iraq's Kurdistan region.

Britain is looking urgently at resuming aid drops after Sunday's aborted missions. But Andrew Robathan, the former Tory armed forces minister, said Britain would have to become involved in military strikes against Isis forces.

Robathan told the World at One on BBC Radio 4: "There can be no real help for the people of Iraq that are threatened by [Isis] without stopping [its] advance. That is what anybody who is worried about the humanitarian situation has to admit.

"We have to realise it is no good just sending aid. The real solution is to stop these people and hopefully allow the Iraqis and the Kurds to defeat them. There are many ways one could use military strikes – air strikes or the use of drones can be done fairly surgically without putting troops on the ground. We had our fingers pretty badly burnt in Iraq, as did the Americans.

"There is no appetite to have proper ground troops on the ground. However, the idea of a few observers perhaps directing air operations is a slightly different matter."

Downing Street insisted Britain had no plans for direct military involvement. Hammond examined an intensification of air drops after the aborted mission on Sunday night.

The prime minister's spokeswoman said: "We are looking to step up deliveries. The Department for International Development and the MoD are working very closely to make sure there are those aid supplies to go as and when we can deliver them.

"Clearly we will be assessing today with our partners and the team we have in Irbil and the other humanitarian teams working there how we are going to ensure successful drops moving forward."

On Saturday Britain dropped 1,200 reusable water containers providing 6,000 litres of water and 240 solar lanterns that can be used to recharge mobile phones. The solar lanterns are crucial in helping Britain and the US communicate with people on the ground.

An RAF spokesman said: "The ongoing effort to get badly needed supplies to displaced people in northern Iraq continues.

"The safety of the Yazidi community is paramount. With a number of people at the drop sites this morning, the crew made the responsible decision not to carry out the air drop to ensure that the lives of those in the area would not be put at risk. We plan to deliver the next drop as soon as possible."